英语单选,为什么选B?

题目

英语单选,为什么选B?
1. _________ the center of our planetary system was considered as heresy by the church in the Middle Ages.
A. It is the sun and not the earth B. That the sun and not the earth
C. Being the sun and not the earth D. The sun and not the earth

答案

由题目可知：the center 前必有一系动词,that 引导的主语从句that不可省略.