She didn't know back soonA weather he would beB if he will come

She didn't know back soonA weather he would beB if he will come
She didn't know back soon
A weather he would be
B if he will come

She didn't know back soonA weather he would beB if he will come
if 引导的从句不能放在否定之后.所以选A

A
这是一个宾语从句，从句除了表示客观规律以外（例如She said that the earth moves around the sun),从句中的谓语动词的时态要与主句中的谓语动词时态一致。
这道题中主句中的谓语动词是did用的是过去时，所以从句中的谓语动词时态也要用过去时。

A