Lincoln was a good speaker and student of political philosophy.______

单项选择题海洋覆盖了地球表面的71%，是全球生命支持系统的一个基本组成部分。______

A.The ocean covers 71 percent of the earth’s surface and it is a basic component of the global bio-support system.
B.The ocean, which covers 71 percent of the earth’s surface, is a basic component of the global bio-support system.
C.F100ding 71 percent of the earth’s surface, the ocean forms a basic component of the global bio-support system,
D.The ocean, which is a basic component of the global bio-support system，covers 71 percent of the earth’s surface.

单项选择题The cold winter of 1957—1958, when freezing temperatures gripped northern Florida, gave an unexpected opportunity to start the program.______