837.It is required that the students _____ mobile phones in their school,so seldom ______ them using one.
A.not use;will you use
B.should not use;you will see
C.don't use;will you see
D.not use;you will see
838.I lived with my brother this winter and didn't have to pay rent.So I ______ save most of my salary.
A.could
B.would
C.might
D.was able to