问题
Only when class began ______that he hadleft his book at home．
A:Accidently
B:he did realize
C:did he realize
D:had he realized
B:he did realize
C:did he realize
D:had he realized
正确答案是：
同类题型
The______ look on his face suggested thathe had passed the exam.
With a population of over seven million, London is ________ the largest cities of the world
_____ is no doubt ______ you have to remain seated and fasten your seatbelt before the plane lands.