用括号中所给词的适当形式填空。 1. I haven't decided what ________ (write) about. 2. I often hear him________ (sing) in the next room. 3. I find it easy _______ (work) out the difficult problem. 4. It is too dark to see the blackboard________ (clear). you had better turn on the light. 5. — Where is Bob?do you know? — Oh, he (go) to the post office. 6. The teacher is ________ (please) with what we have done in class. 7. Tom ran so ________ (quick) that I couldn't catch up with him.