题目

From space，the earth looks blue.This is ________ about seventy­one percent of its surface is covered by water. A．why                               B．how C．because                           D．whether 答案：C　本题考查表语从句的引导词。句意：从太空看，地球是蓝色的。这是因为它表面大约71%被水所覆盖。首先分析前后两句之间的逻辑关系，此处为“前果后因”，使用because，故选C项。

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