To answer this question, the user needs to have basic knowledge of ABAP programming language and its event-driven programming model.

The correct answer is B. Start-of-selection is the default event in ABAP. This event is triggered when the program is executed and is responsible for fetching data from the database tables and displaying it on the screen.

Now, let's go through each option to explain why it is right or wrong:

A. Initialization: This is not the default event in ABAP. The initialization event is used for initializing variables and internal tables before the start-of-selection event is triggered.

B. Start-of-selection: This is the correct answer. This event is triggered by default when the program is executed.

C. At Selection-screen: This event is triggered when the user interacts with the selection screen of the ABAP program. It is not the default event.

D. Top-of-page: This event is responsible for displaying headers and footers on each page of the ABAP program. It is not the default event.

Therefore, the correct answer is:

The Answer is: B. Start-of-selection