________ is the center of our planetary system was a difficult concept to grasp

游客2024-01-14 45

问题 ________ is the center of our planetary system was a difficult concept to grasp in the Middle Age.

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

解析句意：太阳是星系的中心，而不是地球，在中世纪这是一个难以理解的概念。根据句子结构我们可以看出。在was前面是一个主语从句，而主语从句必须有引导词。但A、B和C中都没有引导词，因此三个均错。D中that引导主语从句，在句中不做任何成分，只起引导词的作用，故选D。

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