求问几道语法题，急！

67. Construction of first skyscraper began in Chicago in 1883 with the ten-story Home Insurance Building.

A和B哪个更错啊！

68. The Mississippi riverboat, which evolved from simpler steamship of the early 1800’s, became the dominant form of passenger transport on the Mississippi River.

D选项不需要用复数吗，单数名词不是不能单独出现吗？

4. Perhaps the most significant postwar trend was the decentralization of cities throughout the United States, _________ when massive highway-building programs permitted greater suburban growth.

A. and accelerated a phenomenon

B. a phenomenon that accelerated

C. accelerating a phenomenon which,

D. the acceleration of which phenomenon

A为什么不对？

多谢答疑，就要考了，还是有一些那不准，急啊！

67. B

68. B

4. A的主语不对。

67. b

68.b--steamships

realx and good luck!!!!!

Construction 不需要复数形式吗？这也是可数名词啊。