Once harm ______ to the environment, it takes years to have the system recovered.
| A．does | B．is done | C．will be done | D．be done |
—Why，I didn’t get you on the phone.
—We ________football on the playground when you phoned.
| A．must be playing |
| B．must play |
| C．must have played |
| D．must have been playing |
—I wonder where Peter is.He said he’d be here for lunch.
—Don’t worry！He________be caught in the rush hour.
| A．will | B．should |
| C．can | D．may |
My mother is a great cook and we ________ never get enough of her cookies.
| A．may | B．need |
| C．should | D．can |
—Could I have a word with you，mum?
—Oh，dear，if you ________.
| A．can | B．must |
| C．may | D．should |
It is important to know about the cultural differences that ________ cause problems.
| A．must | B．dare |
| C．may | D．shall |