— Bob has gone to California.
— Oh, can you tell me when he ______?
| A．has left | B．left | C．is leaving | D．would leaving |
He failed the final examination and only then ____ how much time he had wasted.
| A．he realized | B．had he realized |
| C．he had realized | D．did he realize |
Recently, however, scientists have been finding that long-term use of these fertilizers can cause damage to the land, thus _____it less fertile.
| A．make | B．to make |
| C．made | D．making |
When the area was _______ by the flood, the government organized people to send food and medicine there immediately.
| A．cut away | B．cut down |
| C．cut off | D．cut up |
People should ______the traffic rules when they travel to a new place. Nobody can be exception.
| A．perform | B．observe |
| C．possess | D．support |
So far, some advanced teaching equipment, together with three hundred new books, ______ to those schools in the faraway area.
| A．has been sent | B．have been sent |
| C．was sent | D．were sent |