The river will be dirtier and dirtier________we do nothing to protect them．
| A．since |
| B．if |
| C．unless |
| D．until |
—When can you finish your work?
—I need ______ two hours to finish it.
| A．at last | B．at most |
| C．at once | D．at least |
—Hi, Bob! _____we go for a trip tomorrow?
—Good idea! That sounds fun.
| A．Do | B．Are | C．Shall | D．May |
My son will join in the football game, I will go to _____ him on.
| A．cheer | B．catch | C．bring | D．wish |
—_______do you go skating ?
—Twice a week.
| A．How long | B．How much |
| C．How often | D．How far |
Kate spends an hour ______ swimming every week.
| A．practice | B．practices |
| C．practicing | D．to practice |