______ is the center of our planetary system was a difficult concept to grasp in the Middle Age.答案是That the sun and not the earth.为什么Being the sun and not the earth.不可以呢不是非谓语吗,可以做为主语从句中的主语部分啊

问题描述:

______ is the center of our planetary system was a difficult concept to grasp in the Middle Age.
答案是That the sun and not the earth.
为什么Being the sun and not the earth.不可以呢
不是非谓语吗,可以做为主语从句中的主语部分啊

第一个是主语从句,肯定可以作主语,第二个是一个系表结构怎么可以作主语呢

动名词才可以作主语