单选题
9.
______is the center of our planetary system was a difficult concept to grasp in the Middle Ages.
A、
That the sun and not the earth
B、
It is the sun and not the earth
C、
Being the sun and not the earth
D、
The sun and not the earth
【正确答案】
A
【答案解析】
that引导的从句作主语；B．It is the sun and not the earth引导强调句；D．The sunand not the earth作主语，谓语是is，已是一个完整的句子，后面不能再跟一个谓语动词was。
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