i didn't know ________at that time

问题描述:

i didn't know ________at that time
A.where does he come from
B.if janet will help me with cooking
C.the light travels faster than the sound
D.what was the girl doing

C
从句应该是陈述语序,AD错了
时态应和前面的didn't一致,都是过去时,AB错.C没错,因为C中说的是一般公理或道理,这种不用过去时