I didn’t know he came back __________ I met him in the street . 

We prefer ________at the party rather than______.

I was just falling asleep ____ there was a loud knock at the door.

--I hear Jack Chan will come to Laiwu next week. --Really? _______ he comes, my younger sister will be very happy,

I will take a holiday with my family _______ I finish all the exams.