单选题 ______ is known to all, the moon travels around the earth.
A) As C) Which
B) That D) What

【正确答案】 A

【答案解析】句子意为：众所周知，月亮绕着地球转。这是一个定语从句。当先行词是一个句子且引导词放在句首时，必须用as引导。