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
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
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。