Which is a valid use of errors and warnings in the PeopleCode row action events?

Which is a valid use of errors and warnings in the PeopleCode row action events?

A.
Place an error statement in RowDelete to prevent a row from being deleted.

B.
Place an error statement in RowInsert to prevent a row from being inserted.

C.
Place a warning statement in RowInsert to give the user an opportunity to accept the insert or
cancel it.

D.
Place an error statement in RowInsert to give the user an opportunity to accept the insert or
cancel it.

E.
Place an error statement in RowDelete to give the user an opportunity to accept the delete or
cancel it.