—Why does the river smell terrible
—Because large quantities of water________．
| A．have polluted | B．is being polluted |
| C．has been polluted | D．have been polluted |
The boy burst into tears ________ he saw his mother.
| A．at the moment | B．in a moment | C．for a moment | D．the moment |
________, I could not memorize the text.
| A．However hard did I try | B．However hard I tried |
| C．However I tried hard | D．However I had tried hard |
.Although the teacher did not mention any names, everybody knew who he was
| A．attending to | B．turning to | C．referring to | D．talking to |
You only had meat and fish yesterday. If you had eaten vegetables, theyeasily.
| A．would digest | B．digested | C．will digest | D．would have digested |
The telephone _______, but by the time I got indoors, it stopped.
| A．had rung | B．was ringing | C．rings | D．has rung |