用since,as,when,as soon as,while,if,after,before,until或because 填空.
1..Please wait here ( ) I come back.
2.It is so dark outside ( ) it is raining.
3.( ) everyone is here,let's begin our meeting.
4.( ) I get to Beijing,I will write to you.
5.( ) it rains tomorrow,I will not go to Shanghai.