He studies the subject _____. 

At first, we didn't know about Tom. But ____, we came to know that he was an honest boy.

The conference was _______ fixed for the 10th, August, but later the unexpected landslide(泥石流) in Zhouqu in Gansu province, made us put it off.

Tonny’s parents thought he was at school, but ______ he was in an Internet bar.

If you smoke a cigarette every day, you will _____ become addicted to smoking．