来一个英语高手!Einstein's theory of relativity seemed hard to believe at the time ___.选哪一个?A.when he first introduced B.that he first introduced it C.he first introduced D.which he first introduced it要解释下!
问题描述：
来一个英语高手!Einstein's theory of relativity seemed hard to believe at the time ___.选哪一个?A.when he first introduced B.that he first introduced it C.he first introduced D.which he first introduced it要解释下!
答