Explanation
The automatic account determination is used to assign the correct general ledger accounts for the inventory postings. If the account determination is set up incorrectly, the system will issue an error message when posting a transaction that affects the inventory value or quantity. The transactions C, D, and E are examples of such transactions, as they involve stock movements between different valuation areas, stock types, or company codes. The transactions A and B do not affect the inventory value or quantity, as they only change the material master data or the purchasing info record.References: SAP Help Portal, SAP Community

Explanation
Material requirements planning (MRP) is a process that calculates the net requirements and generates planned orders or purchase requisitions for materials based on various factors, such as demand, supply, lead time, lot size, safety stock, etc. To carry out MRP for a plant, some prerequisites are needed. Two of them are:
Maintain MRP data in the material master record for the materials to be planned automatically: This prerequisite is necessary, as the MRP data contains the parameters that control how the system plans the material, such as MRP type, MRP group, MRP controller, lot size, procurement type, special procurement, etc. Without these parameters, the system cannot determine the optimal quantity and timing of the material requirements.
Maintain plant parameters for the corresponding plant in Customizing: This prerequisite is necessary, as the plant parameters define the global settings that apply to all materials in the plant, such as planning horizon, planning calendar, opening period, scheduling margin key, etc. These settings influence how the system calculates the dates and quantities of the planned orders or purchase requisitions.

Explanation
MRP Live is a planning run that is executed on SAP HANA database using optimized algorithms and parallel processing. It can create two types of procurement proposals for externally procured materials:
Delivery schedule line: This is a line item in a scheduling agreement that specifies the delivery date and quantity for a material.
Purchase requisition: This is an internal document that requests the purchasing department to procure a certain quantity of a material or service by a certain date. References: SAP S/4HANA Sourcing and Procurement | SAP Learning, Course S4525, Unit 1, Lesson 1.