It was said was how the Chinese first raised silk worms.A. that whatB. that whichC. that w

问题补充：

It was said was how the Chinese first raised silk worms.

A. that what

B. that which

C. that who

D. that that

答案：

A. that what

B. that which

C. that who

(答案→)D. that that

解析：本句中的it为形式主语，真正的主语是后面的由that 引导的主语从句that that was how the Chinese first raised silk worms，在这个主语从句中，第一个that 只起引导词的作用，第二个that 是指示代词，作从句的主语。