Chocolate had been once the drink of Mayan and Aztec kings and now a cocoa shortage may make chocolate an exclusive luxury again
A. had been once the drink of Mayan and Aztec kings and now a cocoa shortage may make chocolate
B. was once the drink of Mayan and Aztec kings but now a cocoa shortage may make chocolate
C. had once been the drink of Mayan and Aztec kings and now a cocoa shortage will make chocolate
D. was once the drink of Mayan and Aztec kings and now a cocoa shortage may make chocolate
E. was once the drink of Mayan and Aztec kings although now a cocoa shortage may make chocolate
As this sentence is not trying to present any contrast, answer choices B and E are eliminated.
Use of had is incorrect as there are no two things taking place at different times in the past. Eliminate A and C.
The only answer left is D which indeed is the correct answer.