21.    People are destroying the air by adding _________ to it.
A. pollutants    B. polluters     C. pollution      D. polluted
22.    Nonrenewable energy has negative ______________ on the environment.
A, impact                                   B, benefit                                 C, quality                       D, warning
23.    The overuse of _______ fertilizers and deforestation contribute to global warming
A, chemist                                 B, chemistry                     C, chemical                      D, chemist’s
24.    ____________________ include coal, oil and natural gas.
A, Pollutants                             B, Renewable energy       C, Fossil fuels            D, Chemical fertilizers
25.    The ________ refers to the difference in attitudes or behavior between a younger generation and the older one.
A.  argument    B.  generation gap    C. conflict    D.  disagreement
26.    Living under the same roof with three or four generations can be frustrating because of the lack of space, independence, and the daily ________ 
A. arguments    B.  debates    C. conflicts        D.  quarrel
27.    He shared his father's ________ that people should work hard for their living.
A.  belief    B.  gap    C. arguments    D.  complaint
28.    My parents _________ us advice, but never force us to do what they want.
A.  give    B.  follow    C. provide    D.  take
29.    My grandparents encourage me to __________ my dream to become an engineer
A.  quit    B.  follow    C. improve     D.  awake