一般过去时，由此可知前半句是对过去情况的推测，所以用"情态动词＋have done"形式。could have done表示过去本可以做某事，而实际上却没有做，符合句意。

　　5．If we don't clear away the rubbish regularly, it will just ________.

　　A．accumulate B．advocate

　　C．accomplish D．admit

　　解析：选A　句意：如果我们不经常清理垃圾，那它将会逐渐增加。accumulate意为"积累，逐渐增加"，符合语境。advocate意为"提倡，主张，拥护"；accomplish意为"完成，实现"；admit意为"承认，允许"。

　　6．A new school, which is ________ by Shao Yifu, is being built in the village.

　　A．committed B．financed

　　C．resisted D．rescued

　　解析：选B　句意：那个村子正在建一所新学校，它是由邵逸夫出资的。finance"给......提供资金"，符合语境。

　　7．The government takes ________ measures to call the public to protect the environment.

　　A．appropriate B．anxious

　　C．artistic D．agreeable

　　解析：选A　句意：政府采取恰当的措施来号召公众保护环境。根据语境可知A项正确。appropriate"恰当的，适当的"；anxious"焦急的"；artistic"艺术的，精美的"；agreeable"愉悦的，令人愉快的"。

　　8. (全国卷Ⅱ)It was only after he had read the papers ________ Mr. Gross realized the task before him was extremely difficult to complete.

　　A．when B．that

　　C．which D．what

　　解析：选B　句意：格罗斯先生在读了文件后才意识到他面前的这项任务很难完成。题干是强调句型，强调句型的结构是：It＋be＋被强调部分＋that/who＋其他。此处被强调部分是时间状语从句only after he had read the papers。

　　9．-Mr Li is very popular with his students, for he is kind, humorous and experienced.

　　-No wonder he has such a good ________.

A．institution B．attraction