Select the option that expresses the given sentence in passive voice.
They were preparing banners with different designs for the sports meet.

A

Banners were being prepared by them with different designs for the sports meet.

B

Banners have prepared by them with different designs for the sports meet.

C

Banners had been prepared by them with different designs for the sports meet.

D

Banners were prepared by them with different designs for the sports meet.