-Is Jack on duty today?
-It ____ be him. It’s his turn tomorrow.
| A．mustn’t | B．won’t | C．can’t | D．needn’t |
—I wonder why Tom left without a word.
—He __________ have had some trouble, for he looked dull.
| A．should |
| B．must |
| C．can |
| D．could |
I had just got up and was about to cook my breakfast__________ the telephone rang, but it was hung up __________ I could answer it.
| A．while ； when |
| B．when ； as |
| C．as；after |
| D．when；before |
Swimmers must be very strong in order to build up speed because of the high resistance (阻力)of the water. Runners,__________, must struggle against the heavy resistance of the air and ground.
| A．generally |
| B．similarly |
| C．naturally |
| D．probably |
They're not playing baseball today __________ the rain.
| A．because |
| B．as |
| C．since |
| D．because of |
In some places women are expected to earn money __________ men work at home and raise their children.
| A．but |
| B．while |
| C．because |
| D．though |