用連詞if,when,after,before填空.

題目：

用連詞if,when,after,before填空.
1._____ I came to the check-out,I realized that I had no money with me.
2.We will go to the Summer Palace _____it doesn't rain.
3.I wonder _____ I should wear a hat.
4.I found your coat _____ you left the house.
5._____you helped me with my English,I wouldn't have faild the exam.
6.He always puts the interests of others _____ his own.He is very kind.
7.Turn off the switch _____something goes wrong with the machine.
8.It will be a long time _____we finish reading this book.

解答：

when
if
if
after
if
before
when
before