Mary _________ as a volunteer teacher for 10 years.
| A．works | B．will work | C．worked | D．has worked |
The little boy is only six years old, _________ he can make wonderful model cars.
| A．so | B．or | C．but | D．/ |
Please knock at the door ________ you come into the room.
| A．before | B．after | C．until | D．while |
A tourist will easily lose his way in Beijing ______ he has a map or a guide.
| A．if | B．because |
| C．unless | D．when |
Be quick, ＿＿＿we’ll be late for school.
| A．and | B．or | C．so | D．/ |
--- I won’t go to the party tonight.
--- ______ you told me you would. What’s the matter?
| A．So | B．Or | C．Because | D．But |