Explanation
The sequence in which the constructors will be executed is as follows:
Class constructor of superl. This is because the class constructor is a static method that is executed automatically before the class is accessed for the first time. The class constructor is used to initialize the static attributes and components of the class. The class constructor of the superclass is executed before the class constructor of the subclass, as the subclass inherits the static components of the superclass12 Class constructor of subl. This is because the class constructor is a static method that is executed automatically before the class is accessed for the first time. The class constructor is used to initialize the static attributes and components of the class. The class constructor of the subclass is executed after the class constructor of the superclass, as the subclass inherits the static components of the superclass12 Instance constructor of superl. This is because the instance constructor is an instance method that is executed automatically when an instance of the class is created using the statement CREATE OBJECT.
The instance constructor is used to initialize the instance attributes and components of the class. The instance constructor of the superclass is executed before the instance constructor of the subclass, as the subclass inherits the instance components of the superclass. The instance constructor of the subclass must call the instance constructor of the superclass explicitly using super->constructor, unless the superclass is the root node object12 Instance constructor of subl. This is because the instance constructor is an instance method that is executed automatically when an instance of the class is created using the statement CREATE OBJECT.
The instance constructor is used to initialize the instance attributes and components of the class. The instance constructor of the subclass is executed after the instance constructor of the superclass, as the subclass inherits the instance components of the superclass. The instance constructor of the subclass must call the instance constructor of the superclass explicitly using super->constructor, unless the superclass is the root node object12 References: Constructors of Classes - ABAP Keyword Documentation, METHODS - constructor - ABAP Keyword Documentation

Secondary keys are additional keys that can be defined for internal tables to optimize the access to the table using fields that are not part of the primary key. Secondary keys can be either sorted or hashed, depending on the table type and the uniqueness of the key. Secondary keys have the following characteristics1:
A) Secondary keys must be chosen explicitly when you actually read from an internal table. This means that when you use a READ TABLE or a LOOP AT statement to access an internal table, you have to specify the secondary key that you want to use with the USING KEY addition. For example, the following statement reads an internal table itab using a secondary key sec_key:
READ TABLE itab USING KEY sec_key INTO DATA(wa).
If you do not specify the secondary key, the system will use the primary key by default2.
B) Multiple secondary keys are allowed for any kind of internal table. This means that you can define more than one secondary key for an internal table, regardless of the table type. For example, the following statement defines an internal table itab with two secondary keys sec_key_1 and sec_key_2:
DATA itab TYPE SORTED TABLE OF ty_itab WITH NON-UNIQUE KEY sec_key_1 COMPONENTS field1 field2 sec_key_2 COMPONENTS field3 field4.
You can then choose which secondary key to use when you access the internal table1.
D) Sorted secondary keys do NOT have to be unique. This means that you can define a sorted secondary key for an internal table that allows duplicate values for the key fields. A sorted secondary key maintains a predefined sorting order for the internal table, which is defined by the key fields in the order in which they are specified. For example, the following statement defines a sorted secondary key sec_key for an internal table itab that sorts the table by field1 in ascending order and field2 in descending order:
DATA itab TYPE STANDARD TABLE OF ty_itab WITH NON-UNIQUE SORTED KEY sec_key COMPONENTS field1 ASCENDING field2 DESCENDING.
You can then access the internal table using the sorted secondary key with a binary search algorithm, which is faster than a linear search3.
The following are not characteristics of secondary keys for internal tables, because:
C) Hashed secondary keys do NOT have to be unique. This is false because hashed secondary keys must be unique. This means that you can only define a hashed secondary key for an internal table that does not allow duplicate values for the key fields. A hashed secondary key does not have a predefined sorting order for the internal table, but uses a hash algorithm to store and access the table rows. For example, the following statement defines a hashed secondary key sec_key for an internal table itab that hashes the table by field1 and field2:
DATA itab TYPE STANDARD TABLE OF ty_itab WITH UNIQUE HASHED KEY sec_key COMPONENTS field1 field2.
You can then access the internal table using the hashed secondary key with a direct access algorithm, which is very fast.
E) Secondary keys can only be created for standard tables. This is false because secondary keys can be created for any kind of internal table, such as standard tables, sorted tables, and hashed tables. However, the type of the secondary key depends on the type of the internal table. For example, a standard table can have sorted or hashed secondary keys, a sorted table can have sorted secondary keys, and a hashed table can have hashed secondary keys1.

Explanation
In a RESTful Application Programming (RAP) application, you can bind a CDS view to create a value help in the following objects:
Data model view: A data model view is a CDS view that defines the data structure and the associations of an entity in the RAP application. You can use the annotation @Consumption.valueHelpDefinition to bind a value help provider CDS view to an element of the data model view. The value help provider CDS view must contain the key fields of the value help entity and the fields that are displayed in the value help dialog. The value help annotation specifies the entity name, the element name, and optionally the additional binding conditions for the value help provider1.
Metadata Extension: A metadata extension is a CDS view that extends the metadata of another CDS view without changing its data structure. You can use the annotation @MetadataExtension.extendView to specify the target CDS view that you want to extend. You can then use the same annotation
@Consumption.valueHelpDefinition to bind a value help provider CDS view to an element of the target CDS view. The metadata extension allows you to add value help definitions to existing CDS views without modifying them2.
Projection View: A projection view is a CDS view that defines the projection of another CDS view. You can use the annotation @AbapCatalog.sqlViewType: #PROJECTION to specify that the CDS view is a projection view. You can then use the same annotation @Consumption.valueHelpDefinition to bind a value help provider CDS view to an element of the projection view. The projection view allows you to add value help definitions to projected elements of another CDS view3.
You cannot bind a value help provider CDS view to a behavior definition or a service definition, because these objects do not define the data structure or the metadata of an entity in the RAP application. A behavior definition defines the behavior and the validation rules of an entity, such as the create, read, update, and delete (CRUD) operations, the draft handling, the authorization checks, and the side effects4. A service definition defines the service exposure and the service binding of an entity, such as the protocol, the version, the namespace, and the service name5.
References: 1: Value Help with Additional Binding | SAP Help Portal 2: Metadata Extensions - ABAP Keyword Documentation 3: Projection Views - ABAP Keyword Documentation 4: Behavior Definition - ABAP Keyword Documentation 5: Service Definition - ABAP Keyword Documentation

Explanation
The following are the explanations for each statement:
A: This statement is correct. go_subl = CAST #(go_super) will not work. This is because go_subl is a data object of type REF TO cl_subl, which is a reference to the subclass cl_subl. go_super is a data object of type REF TO cl_super, which is a reference to the superclass cl_super. The CAST operator is used to perform a downcast or an upcast of a reference variable to another reference variable of a compatible type. A downcast is a conversion from a more general type to a more specific type, while an upcast is a conversion from a more specific type to a more general type. In this case, the CAST operator is trying to perform a downcast from go_super to go_subl, but this is not possible, as go_super is not pointing to an instance of cl_subl, but to an instance of cl_super. Therefore, the CAST operator will raise an exception CX_SY_MOVE_CAST_ERROR at runtime12 B: This statement is incorrect. go_sub2 = CAST #(go_super) will work. go_subl = CAST #(go_super) will not work. This is because go_sub2 is a data object of type REF TO cl_sub2, which is a reference to the subclass cl_sub2. go_super is a data object of type REF TO cl_super, which is a reference to the superclass cl_super. The CAST operator is used to perform a downcast or an upcast of a reference variable to another reference variable of a compatible type. A downcast is a conversion from a more general type to a more specific type, while an upcast is a conversion from a more specific type to a more general type. In this case, the CAST operator is trying to perform a downcast from go_super to go_sub2, and this is possible, as go_super is pointing to an instance of cl_sub2, which is a subclass of cl_super.
Therefore, the CAST operator will assign the reference of go_super to go_sub2 without raising an exception. However, the CAST operator will not work for go_subl, as explained in statement A12 C: This statement is incorrect. go_sub2 = CAST #(go_super) will work. go_sub2->sub2_meth1(...) will not work. This is because go_sub2 is a data object of type REF TO cl_sub2, which is a reference to the subclass cl_sub2. go_super is a data object of type REF TO cl_super, which is a reference to the superclass cl_super. The CAST operator is used to perform a downcast or an upcast of a reference variable to another reference variable of a compatible type. A downcast is a conversion from a more general type to a more specific type, while an upcast is a conversion from a more specific type to a more general type. In this case, the CAST operator is trying to perform a downcast from go_super to go_sub2, and this is possible, as go_super is pointing to an instance of cl_sub2, which is a subclass of cl_super.
Therefore, the CAST operator will assign the reference of go_super to go_sub2 without raising an exception. However, the method call go_sub2->sub2_meth1(...) will not work, as sub2_meth1 is a subclass-specific method of cl_sub2, which is not inherited by cl_super. Therefore, the method call will raise an exception CX_SY_DYN_CALL_ILLEGAL_METHOD at runtime123 D: This statement is correct. go_subl->subl_meth1(...) will work. This is because go_subl is a data object of type REF TO cl_subl, which is a reference to the subclass cl_subl. subl_meth1 is a subclass-specific method of cl_subl, which is not inherited by cl_super. Therefore, the method call go_subl->subl_meth1(...) will work, as go_subl is pointing to an instance of cl_subl, which has the method subl_meth1123 References: NEW - ABAP Keyword Documentation, CAST - ABAP Keyword Documentation, Method Call - ABAP Keyword Documentation