12.    You should get a plumber ……………the pipes in your bathroom.
A. to check            B. check            C. checking        D. check
13.    Ba is tired …………… he stayed up late watching TV .
A. because            B. as            C. since            D. A,B, and C are correct
14.    The air in the city is very ............................
A. pollute            B. pollution        C. polluted        D. pollutant
15.    If the disaster................in an area, people from other areas will offer help.
A. happens            B. will happen        C. happening        D. would happen
17.    I live in Da Lat, .............is one of the most beautiful cities of Vietnam.
A. who                  B. which                 C. whom                 D. whose