问题补充：
It is said has been translated into Chinese.
A. that
B. which
C. that which
D. that that
答案：
A. that
B. which
C. that which
(答案→)D. that that
解析：当宾语从句的主语是that时，that不可以省略
People say that that was how the Chinese first raised silkworms.据说那就是中国人怎样最先开始养蚕的。
