Every possible means ________ to prevent the air pollution，but the sky is still not very clear.
| A．were using | B．have used |
| C．has been used | D．was used |
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 |
The PLA man saved the boy ____ death.
| A．of | B．from | C．to | D．on |
The group is made up____five students. And they are studying hard to make up____ the lost time.
| A．of,of | B．for,for | C．of,for | D．for,of |