1．The physics teacher was standing by the desk, explaining the exercise _____ the students had done at home.
A．/ B．to C．for D．with
2．Harward, _____ in 1636 , is one of the most famous universities in the U.S.
A．set B．found C．discovered D．founded
3．Do you know what has _____ him?
A．become B．become as C．become of D．become into
