题目

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：D 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。

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