1.You_____________ (无论多么小心都不为过) when you drive a car.

cannot be too careful
解析:本题考查对cannot…too…结构的掌握。cannot…too…意为“无论…都不为过”，具有肯定的含义。相似的句子 还有：A woman cannot have too many hats while a man cannot have too many ties．(女人不嫌帽子多，男人不嫌领带多。)

2.She never dreams of________________(梦见有机会) for her to be sent abroad very soon.

dreams of there being a chance
【解析】本题考查对短语dream of、there be句型和动名词的掌握。“梦见，梦到”用dream of表示，后常接动名词作宾语。 There is sth．for sb．表示“某人有某物”，故表示“她有机会”应该用there is a chance for her；而dream of后面要求接动名词作宾语，故应将is改成being。另外，句尾的不定式是作a chance的定语，表示“被派往国外的机会”。

3.When he arrived, he found______________( 只有老年人和生病的人) at home.

none but the aged and the sick/only the aged and the sick
【解析】本题考查none but结构及形容词名词化用法的掌握。none but…意为“仅仅，只”。“定冠词the+形容词”可以表示一类人。类似的用法还有：the wealthy(富人)，the poor(穷人)，the handicapped(残疾人)等。

4.All flights_________ (因暴风雪而取消), we decided to take the train.

having been canceled because of the snowstorm
解析:本题考查对独立主格结构的掌握。前后分句主语不同且没有连接词，所以考虑用独立主格做状语表示原因。独立结构的构成方式为：名词/代词(与句子的主语不同)+分词/形容词/副词/不定式/介词(短语)。flights与cancel之间是被动关系，且cancel这一动作发生在主句谓语decided的动作之前，所以谓语部分应用分词的被动完成式.

5.The writer_____________ (如此专心致志地写作) that he forgot to tap the ashes from his cigar.

was so absorbed in his writing
解析:本题考查对短语be absorbed in sth．/doing sth．的掌握，该短语意为“全神贯注于…，专心于…”。so强调程度深，与that构成so…that…句型，表示“如此…以至于…”.