It was the first time that Mary _____a play , so she felt a little nervous.
| A．has taken | B．had taken |
| C．would taken | D．was taking |
If you had told him the truth, he ______ so angry now．
| A．isn't | B．wasn't |
| C．wouldn't be | D．wouldn't have been |
Teaching is a difficult job ______ requires great skill and patience．
| A．which | B．where |
| C．who | D．why |
Drivers must stop when the traffic lights _____ red．
| A．turn | B．will turn |
| C．turned | D．were turning |
There was an excited expression ______ his face when he heard the good news．
| A．of | B．on |
| C．at | D．over |
Milk will turn sour soon on hot days ______ it is stored in the refrigerator．
| A．since | B．until |
| C．because | D．unless |