THE CITY _____ AT ONE TIME PROSPEROUS, FOR IT ENJOYED A HIGH LEVEL...

19. - DE THI ANH LOP 11 DE THI 11
DE THI ANH LOP 11 DE THI 11

19. The city _____ at one time prosperous, for it enjoyed a high level of civilization.

A. must have been B. can have been

C. may have been

D. was