—Why does the lake smell terrible?
—Because large quantities of water ________.
| A．have polluted | B．is being polluted |
| C．has been polluted | D．have been polluted |
The stone bridge __ _last year is very beautiful.
| A．built | B．was built | C．being built | D．to be built |
He asked us to him ______ carrying through their plan.
| A．assist; with | B．help; to | C．assist; in | D．help; with |
Only after my friend came ___________________________.
| A．did the computer repair | B．he repaired the computer |
| C．was the computer repaired | D．the computer was repaired |
While ________ to foreigners，you must try your best to make yourself ________.
| A．spoken…understood | B．spoken…understand |
| C．speaking…understood | D．speaking…understand |
The computer system _____ suddenly while he was searching for information on the Internet.
| A．broke down | B．broke out | C．broke up | D．broke in |