----How unhappy your roommate looks!
----Yes，but he’s not willing to tell me what it is____ is troubling him.
| A．what | B．which | C．as | D．that |
I agree ____ what you said.
| A．to | B．on | C．with | D．at |
He wrote the article ____ three days.
| A．at | B．in | C．on | D．by |
He will return____ three o'clock.
| A．after | B．in | C．on | D．at |
He went to Beijing and returned ____ three days.
| A．in | B．before | C．later | D．after |
He will come ____ three days.
| A．before | B．after | C．in | D．later |