You _____ such a serious mistake if you had followed his advice.
| A．may not make | B．might not make |
| C．shouldn’t have made | D．might not have made |
environmental damage is done, it takes many years for the ecosystem（生态系统）to recover.
| A．Even if |
| B．If only |
| C．While |
| D．Once |
____, he talks a lot about his favorite singers after class.
| A．A quiet student as he may be |
| B．Quiet student as he may be |
| C．Be a quiet student as he may |
| D．Quiet as he may be a student |
You must keep on working in the evening, you are sure you can finish the task in time.
| A．as |
| B．if |
| C．when |
| D．unless |
--Did Jack come back early last night？
--Yes.It was not yet eight o'clock_____he arrived home.
| A．before |
| B．when |
| C．that |
| D．until |
I’d like to arrive 20 minutes early I can have time for a cup of tea.
| A．as soon as |
| B．as a result |
| C．in case |
| D．so that |