1. It is not easy ____ the answer to the difficult math problem.

　　A. to figure out B. figuring out C. figure out D. being figured out

　　【答案】A. 本題考查的是it 作形式主語，真正的主語是to do.這種句型很常見，例如：It's difficult to find a job these days. 如今找一份工作很難。

　　2. He has already made up his mind. It's no use_____ him.

　　A. try to persuade B. trying to persuade

　　C. to try to persuade D. to try persuading

　　【答案】B It is no use doing sth.“作某事沒有用”是固定搭配。Ing做真正主語。

　　3. ____ is one of good properties of this metal.

　　A. Light in weight B. Having been light in weight

　　C. Be light in weight D. Being light in weight

　　【答案】D 主語應(yīng)該是名詞性質(zhì)，因此排除A項(xiàng)，因?yàn)閘ight 是形容詞;也排除C 項(xiàng)，be light in weight 不能作為名詞詞性;而此句陳述的是客觀真理，應(yīng)該用一般現(xiàn)在時而不是完成時， 所以選D項(xiàng)。D項(xiàng)意為“質(zhì)量輕 ”，in 表示“在某方面 ”，weight “質(zhì)量，重量 ”;句意為“重量輕是這種金屬的優(yōu)良特征之一。”

　　4. It's necessary for them ____ another chance.

　　A. to give B. to be given C. being given D. giving

　　【答案】B 再給他們一次機(jī)會是很重要的。不定式作主語。

　　5. It's necessary to be prepared for a job interview. ________ the answers ready will be of great help.

　　A. To have had B. Having had C. Have D. Having

　　【答案】D 面試之前有必要做好準(zhǔn)備，提前準(zhǔn)備好答案會很有幫助。Ing形式做主語。