1.Perhaps the most significant postwar trend was the decentralization of cities thoughout the US,_____when massive highway-building programs permitted greater suburban growth.
A,and accelerated a phenomenon . B , a phenomenon that accelerated
偶选Ａ可是答案是B,B在句中是啥成分阿？？
2.Ronald Reagan had served two terms as governor of California before____President.
A,he became B,became
before后面到底加什莫？可以加句子吗？句子的主语可以省吗？
3。Because of __________diversity,seven separate groupings or divisions of algae have been established by botanists.
A,their B,those
为啥those不行啊？应该后者更好啊，前面又没有提范围？
4。Because Mars is farther from the Sun than____,Mars takes longer to complete a revolution
A.Earth is B.is from Earth. C,what is Earth D, is it Earth
不是than后要到装吗，咋不到装选第一个拉阿c为啥也不对阿
谢谢啦… | 
