Every possible means ________ to prevent the air pollution , but the sky is still not clear.
| A．is used | B．are used | C．has been used | D．have been used |
The students expected there ________ more free time before the test.
| A．is | B．have been | C．to be | D．being |
They tried to prevent the damage ________ their cattle.
| A．from protecting | B．protecting | C．protect | D．to protect |
His father disappeared, ________ two children and never _______ from again.
| A．left; being heard | B．leaving; heard | C．left; be heard | D．leaving; to be heard |
Does the way you thought of ________ the water clean make any sense?
| A．making | B．to make | C．how to make | D．having made |
In order not to be disturbed, I spend three days _______ in my study.
| A．locking | B．locked | C．to lock | D．lock |