第二节：完形填空（共20小题，每小题1.5分，满分30分）阅读下面短文，从短文后各题所给的四个选项（A、B、C和D）中，选出可以填入空白处的最佳选项，并在答题卡上将该项涂黑。
Man-made Causes
Man-made causes probably do the most damage. There are many man-made causes.  21  is one of the biggest man-made problems. Pollution  22  in many shapes and sizes. Burning fossil fuels is one thing that causes pollution. Fossil(化石) fuels(燃料)are fuels made of organic matter such as coal, or oil. when fossil fuels are burned they  23  a green house gas called CO2. Also mining coal and oil allows methane to escape. How does it escape? Methane(甲烷)is  24  in the ground.  25  coal or oil is mined you have to dig up the earth a little. When you dig up the fossil fuels you dig up the methane as well.
Another major man-made  26  of Global Warming is population. More people  27  more food, and more methods of transportation, right? That means more methane because  28  will be more burning of fossil fuels, 29  more agriculture. Now you’re probably thinking, “Wait a minute, you said agriculture is going to be damaged by Global Warming, but  30  you’re saying agriculture is going to help cause Global Warming?” Well, have you  31 been in a barn filled with animals and you smell something  32 ? You re  33  methane. Another source of methane is manure. Because more food is needed we have to raise food. Animals like cows are a source of food which means more manure and methane. Another problem  34  the increasing population is  35 . More people means more cars, and more cares means more pollution. Also, many people have more than one car.
Since CO2 contributes to global warming, the increase in population makes the problem worse because we breathe out CO2.  36 , the trees that change our CO2 to oxygen are being demolished because we’re using the land that we cut the trees down from as property  37 our homes and buildings. We are not replacing the trees(an important part of our ecosystem), so we are  38  taking  39  of our natural resources and giving nothing back in  40 .
21．A．Pollution            B．Damage               C．Fossil           D．Transportation
22．A．goes                   B．comes                 C．takes            D．moves
23．A．give off                    B．look out               C．burn away     D．take in
24．A．originally           B．mostly                 C．naturally       D．usually
25．A．Because             B．When                  C．While           D．But
26．A．reason                B．excuse                 C．cause            D．problem
27．A．eats                    B．takes                   C．produces       D．means
28．A．it                        B．there                   C．that               D．they
29．A．and                           B．or                        C．though         D．but
30．A．then                   B．there                   C．before          D．now
31．A．ever                   B．yet                      C．still               D．even
32．A．Pleasant             B．terrible                C．sweet           D．nice
33．A．feeling               B．using                   C．looking        D．smelling
34．A．of                       B．as                        C．with                    D．for
35．A．pollution            B．population          C．warming             D．transportation
36．A．Also                   B．However             C．Therefore      D．Thus
37．A．as                       B．for                       C．like               D．to
38．A．quickly               B．constantly           C．surely           D．usually
39．A．use                      B．part                      C．hold                    D．advantage
40．A．return                 B．turn                      C．general         D．total