几道用所给词的适当形式填空
l（               ）(not,know)what to do,he decided to ask a policeman.
On (             ) (learn) the result of the final exam,the boy decided to work harder.
Tom is not here.He(           )(go) to London on a business trip.
This small town(            )(develop) into a large city.
I(          )(read) the newspaper the whole afternoon.
The man took the money and (              )(leave) in a great hurry.
The students (           )(call on) professor Smith in his office after he (          )(return).