A) some time C) sometime
B) some times D) sometimes

A．express
B．show
C．imply
D．mean

A．Zoos play an important role in educating people about the conservation of wildlife and plants.
B．Zoos are a good device against species extinction.
C．Zoos valuable role in society is still an issue in debate.
D．Zoos are regularly visited by most city people.