We are sure they'll come to help us_______they are free.Boys and girls,hand in your exercies-books_______you go home.______the bell rang,she was waiting in her seat.
问题描述：
We are sure they'll come to help us_______they are free.Boys and girls,hand in your exercies-
books_______you go home.
______the bell rang,she was waiting in her seat.
答
if
before
When
答
when；
before；
when