It is only 　　　　 people know the importance of science 　　　　 science can really serve the pe

问题补充：

It is only people know the importance of science science can really serve the people.

A. that； when

B. when； that

C. then； that

D. that； then

答案：

A. that； when

(答案→)B. when； that

C. then； that

D. that； then

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