Fleming discovered penicillin almost by______.
| A．experiment | B．hand | C．accident | D．theory |
Helen didn’t mention anything about the dinner over the phone; she seemed about our appointment.
| A．to have forgotten | B．to forget |
| C．having forgotten | D．forgetting |
Many people see the computer as a “magic box”, and are not concerned with ______ it works.
| A．that | B．whether | C．how | D．if |
There are two rooms on the first floor, is used as a reception room.
| A．a smaller of which | B．a smaller of them |
| C．of which the smaller | D．the smaller of them |
—No one can achieve anything of real significance he works very hard.
— I got it, Dad. I’ll study hard from now on.
| A．because | B．if | C．unless | D．when |
It was his ability to deal with unexpected problems rather than his family background drew the manager’s attention.
| A．where | B．which | C．what | D．that |