The correct answer is B. eventtype=web_errors.
An event type is a way to categorize events based on a search. An event type assigns a label to events that match a specific search criteria. Event types can be used to filter and group events, create alerts, or generate reports1.
To search for events that have a specific event type, you need to use the eventtype field with the name of the event type as the value. The syntax for this is:
eventtype=<event_type_name>
For example, if you want to search for events that have the event type web_errors, you can use the following syntax:
eventtype=web_errors
This will return only the events that match the search criteria defined by the web_errors event type.
The other options are not correct because they use different syntax or fields that are not related to event types.
These options are:
* A. tag=web_errors: This option uses the tag field, which is a way to add descriptive keywords to events based on field values. Tags are different from event types, although they can be used together. Tags can be used to filter and group events by common characteristics2.
* C. eventtype "web errors": This option uses quotation marks around the event type name, which is not valid syntax for the eventtype field. Quotation marks are used to enclose phrases or exact matches in a search3.
* D. eventtype (web_errors): This option uses parentheses around the event type name, which is also not valid syntax for the eventtype field. Parentheses are used to group expressions or terms in a search3.
References:
* About event types
* About tags
* Search command cheatsheet

Reference: https://docs.splunk.com/Documentation/Splunk/8.0.3/Knowledge/Aboutdatamodels Data models are collections of datasets that represent your data in a structured and hierarchical way. Data models define how your data is organized into objects and fields. Data models can be composed of one or more of the following datasets:
Events datasets: These are the base datasets that represent raw events in Splunk. Events datasets can be filtered by constraints, such as search terms, sourcetypes, indexes, etc.
Search datasets: These are derived datasets that represent the results of a search on events or other datasets.
Search datasets can use any search command, such as stats, eval, rex, etc., to transform the data.
Transaction datasets: These are derived datasets that represent groups of events that are related by fields, time, or both. Transaction datasets can use the transaction command or event types with transactiontype=true to create transactions.

The search below would limit an "alert" tag to the "host" field.
tag::host=alert
The search does the following:
It uses tag syntax to filter events by tags. Tags are custom labels that can be applied to fields or field values to provide additional context or meaning for your data.
It specifies tag::host=alert as the tag filter. This means that it will only return events that have an "alert" tag applied to their host field or host field value.
It uses an equal sign (=) to indicate an exact match between the tag and the field or field value.

The correct answer is B. The value for the productName field because it appears first.
The coalesce function is an eval function that takes an arbitrary number of arguments and returns the first value that is not null. A null value means that the field has no value at all, while an empty value means that the field has a value, but it is "" or zero-length1.
The coalesce function can be used to combine fields that have different names but represent the same data, such as IP address or user name. The coalesce function can also be used to rename fields for clarity or convenience2.
The syntax for the coalesce function is:
coalesce(<field1>,<field2>,...)
The coalesce function will return the value of the first field that is not null in the argument list. If all fields are null, the coalesce function will return null.
For example, if you have a set of events where the IP address is extracted to either clientip or ipaddress, you can use the coalesce function to define a new field called ip, that takes the value of either clientip or ipaddress, depending on which is not null:
| eval ip=coalesce(clientip,ipaddress)
In your example, you have a set of events where the product name is extracted to either productName or productid, and you use the coalesce function to define a new field called productINFO, that takes the value of either productName or productid, depending on which is not null:
| eval productINFO=coalesce(productName,productid)
If both productName and productid fields have values for a given event, the coalesce function will return the value of the productName field because it appears first in the argument list. The productid field will be ignored by the coalesce function.
Therefore, the value for the productName field will be used to populate the productINFO field if both fields have values for a given event.
References:
* Search Command> Coalesce
* USAGE OF SPLUNK EVAL FUNCTION : COALESCE