It is known to us __________ it was not until 1938 ________ the first colour TV programme began to be broadcast in the world.

A．that, which

B．/, /

C．that, that

D．which, that

转化入炉蒸汽流量调节阀卡，应（）

A、降低进料

B、用上游阀控制

C、调整PID参数

D、改副线控制