答案与解析：A　call on sb.拜访某人；drop in on sb. 拜访某人；drop out脱离；退出，退学；call at到......作短暂访问；停靠。理解句意可知答案是A项。

4．The blue whale，________biggest animal that has ever lived on this planet，is in________danger of dying out.

A．a；the B．the；the

C．a；/ D．the；/

答案与解析：D　形容词最高级前用定冠词the；in danger of ...在......危险中。

5．________much is known about what occurs during sleep，the precise function of sleep and its different stages remain largely in the realm of assumption.

A．Because B．For

C．Since D．While

答案与解析：D　分析题目可知句中"much is known"与"remain largely in the realm of assumption"，故答案是D项：while conj. 虽然(放在句首)；然而。

6．________into a great port，Qingdao plays an important part in the________of the province.

A. Developed；developing

B. Developing；developed

C. To develop；develop

D. Developed；development

答案与解析：D　句意：青岛已经发展为一个大港，在省内的发展中起着重要的作用。根据句意可判断第一空格处用过去分词作状语，第二个空格处用名词，in the development of...在......的发展中。

7．________it rains when we can't find a place to escape from the rain?

A．What if B．How come

C．What about D．How about

答案与解析：A　理解句意可判断答案是A项：what if conj. "假使......呢？；若是......又怎么样？"，意思等于：What will or would happen if......？如果(假如)......将会怎么样？

8．Years later，these islands united as one，________a new nation.

A．formed B．to be formed

C．be formed D．forming

答案与解析：D　此处是分词作结果状语。因islands与form是主动关系，故用现在分词

9．You can fly to New York this afternoon________you don't mind changing planes in San Francisco.

A．as long as B．as far as