There is no doubt________man will continue to explore the vast universe in the future, but the rate at

which we approach depends on the development of technology.[ ]

A. whether     

B. what

C. when

D. that

我国一般把井深在（）的井定义为深井。

A.3000—4500m

B.4000—4500m

C.4550—5500m

D.4000—6000m