我们练习里有一题:It was in 1969____the American astronaut succeeded in landing on the moon A.that Bwhich Cwhen D in which 我们老师说答

我们练习里有一题:It was in 1969____the American astronaut succeeded in landing on the moon A.that Bwhich Cwhen D in which 我们老师说答案是A 我觉得是C 她说是It be+被强调部分的结构 但我在课外书看过这句话 ..
It was in 1937 when Japanese soldiers broke into the city Beiping.
谁能帮我解释下/.