Question

From space, the earth looks blue. This is      about seventy-one percent of its surface is covered by water.

A．why

B．how

C．because

D． whether

Answer 1

C

解析试题分析：根据句意：地球看起来是蓝色的。这是因为其表面71%是被水覆盖的。这里使用的是表语从句，This is because那就是因为…，This is why…那就是为什么…，所以选C。
考点：考查表语从句。