状语从句的问题？

qinxing

Direct information on the chemical composition of the moon because available in  1969__ of the first Apollo mission to land on the Moon.

A.with the  return

B,returning

c.when returned

D.and the return

此题的解释是（空格前后完整？because 后没有主胃呀，是不是省拉。还有because 前面没有主语，谓语是不是direct)。为什么答案B 和C怎么不行。

consonant

because->became

key:A

C，=when it (Direct information) is returned of the ....错

qinxing

为何不选B

consonant

returning of...和前边怎么连的起来？