四六级考试

【单选题】 ______ is the center of our planetary system was a difficult concept to grasp in the Middle Ages.
A．It is the sun and not the earth
B．Being the sun and not the earth
C．The sun and not the earth
D．That the sun and not the earth

网考网参考答案：D
网考网解析：
语法结构题。此题考查主语从句。首先应判断出本句主句的谓语是was，其主语为一个真理性的陈述句。当句子的主语是一个陈述句时，必须由从属连词that来引导。因此[D]项符合题意。 查看试题解析出处>>