It was 1969 the American astronauts succeeded in landing on the moon. AthatBwhen C.

问题补充：

It was 1969 the American astronauts succeeded in landing on the moon.

Athat

Bwhen

Con which

Dwhich

答案：

A. that

(答案→)B. when

C. on which

D. which

解析： when 引导定语从句修饰时间1969 。1969前加上介词in可以选A ，此时是强调句。