问题
选择题
______ is even more important is that the earth cooled down, water began to appear on its surface.
A．When
B．That
C．Which
D．What
答案
答案：D
本题考查名词性从句。句中What引导去主语从句，并在句中做主语。句意：甚至更为重要的是，地球变暖，水开始出现在它的表面。
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