Something must be done to prevent factories       poisonous gases so as to keep the city       .

       A．sending out; from polluting

       B．send out, polluting

       C．from sending out; from polluting

       D．sending out; from being polluted

Something must be done to prevent factories ________ poisonous gases so as to keep the city ________.

[　　]

A．sending out; from polluting

B．send out; polluting

C．from sending out; from polluting

D．sending out; from being polluted

Something must be done to prevent factories sending out poisonous gases so as to keep the city _________.

A polluting          B. from polluting    C. pollute          D. from being polluted

Something must be done to prevent factories sending out poisonous gases so as to keep the city _________

1. A.
   polluting
2. B.
   from polluting
3. C.
   pollute
4. D.
   from being polluted

Something must be done to prevent factories sending out poisonous gases so as to keep the city _________.
A polluting          B. from polluting    C. pollute          D. from being polluted