______is the center of our planetary system was a difficult concept to grasp in

游客2023-11-16 39

问题 ______is the center of our planetary system was a difficult concept to grasp in the Middle Ages.

选项 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

答案 D

解析名词性从句。主句是一个系表结构的句子，系动词是was，表语是a difficult concept，那么充当主语的就是was之前的句子，即主语从句，由that引导，正确答案为D。

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