Every _____ hundred metres, there are watch towers, _____soldiers _____keep watch.

A. a few, where, used to

B. few, where, used to

C. few, which, used to

D. a few, which, were used to

Every _____ hundred metres, there are watch towers, _____soldiers keep watch.

A. a few, where, used to　　　　 B. few, where, used to

C. few, which, used to　　　　 D. a few, which, were used to