_____ to gain access to seats at college ______ the seniors are

_____ to gain access to seats at college ______ the seniors are working hard.
A、That is;\
B、It is;that
C、What is;that
D、Which is;why
【正确答案】：B
【题目解析】：考查名词性从句的用法。此处it是形式主语，that the seniors are working hard是真正的主语从句。