Something must be done to prevent our city ____ by thick smoke.
| A．to be polluted | B．from polluting | C．from being polluted | D．polluting |
.A great number of students said they were forced to practise the piano.
| A．to question | B．to be questioned |
| C．questioned | D．questioning |
I like _____ in spring when everything turns green and active.
| A．one | B．it | C．that | D．this |
You can imagine what difficulty we had __________ home in the snowstorm.
| A．walked | B．walking | C．to walk | D．walk |
We hurried to the station, ________ the train was gone.
| A．to find | B．finding | C．found | D．only to find |
.Operation rooms should be kept free ______ bacteria of any kind.
| A．with | B．for | C．from | D．to |