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______ people have become masters of their country ____ science can really serve the people.

   A.It is only then ;that         B.It is that;when

   C.It is only when; that         D.It is when;when

______ people have become masters of their country ____ science can really serve the people.

_______ the people have become masters of their country _______ science can really serve the people.

A. It is only then; that ?

B. It was that; when?

C. It is only when; that

D. It was when; then?

30．       the people have become masters of their own country that science can really serve the people.

         A．Only then   B．It is only when   C．Only when D．It is only then