1,The girl had a short rest and did her homework ------ she

1,The girl had a short rest and did her homework ______ she reached home.
A.after B.before C.when D.since
2.78.If you miss so many lessons,you must fall behind ____ classmates.
A.another B.the others C.other D.the other
第一题答案是C,为什么?
第二题选什么?
到底选哪个?第二题答案说选D,我觉得如果把D理解成"剩下同学中的一些"也可以,因为并不是不学习就会落后于所有同学,其他同学不是也没学习的,所以只是落后于一些