Past tense vs Past Perfect tense

Some buildings that were destroyed and heavily damaged in the earthquake last year were constructed in
violation of the city's building code.

(A) Some buildings that were destroyed and heavily damaged in the earthquake last year were
(B) Some buildings that were destroyed or heavily damaged in the earthquake last year had been
(C) Some buildings that the earthquake destroyed and heavily damaged last year have been
(D) Last year the earthquake destroyed or heavily damaged some buildings that have been
(E) Last year some of the buildings that were destroyed or heavily damaged in the earthquake had been

OA B

I got confused whether we really needed to use past perfect.. We could have used simple past
DId we really needed to emphasize on past perfect here

what if the answer choice A was A)Some buildings that were destroyed or heavily damaged in the earthquake last year were

Please explain..

Also for an exampe from mgmt guides
joe learned about an epoch in which dinosaurs had walked the earth -- INCORRECT
joe learned about an epoch in which dinosaurs walked the earth -- CORRECT
[/u]