I often do my homework ____ the computer.
---Where is the scientist ________ gave us the talk yesterday?---He has gone back to Qinghua University.
The letter _______ I received from him yesterday is very important.
---Does the teacher know everybody _______ planted the trees?·---Yes, he does.
I don’t know if he tomorrow. If he , I’ll meet him.
We won’t put off our plan __________ it snows heavily tomorrow.