21. It came as__________shock to learn that Bob，one of the top students in our class,failed in __________ exam.
A. ／；the B. a；the C. a；an D. ／；an
22. —Could I use your cellphone to make a call,Jake?
—Sorry. It__________in the office.
A. is charging B. has charged C. is being charged D. has been charged
