＿＿＿the people have bee the master of their own 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
网友回答
A. It is only then； that
B. It was that； when
(答案→)C. It is only when； that
D. It was when； then
解析：该题为强调句型，强调only when引导的时间状语从句。