＿＿＿the people have become 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

膨胀阀内有一（）由隔热物包围，可使挥发器之出气温度，完全影响开关之作用。