近亲结婚对后代的影响是( )。
A．遗传病连代传递
B．产生交叉遗传
C．增加隐性遗传病的发病率
D．出现返祖现象
参考答案：C
解析： 近亲婚配是指直系血亲和三代以内的旁系血亲这种的婚配。近亲结婚可以使隐性致病基因相遇的机会明显增加，隐性遗传病的发病率也随之增加。研究表明，每个人身上都有大约5～6种隐性致病基因，这种基因只有在成对的情况下才会发病。故选C。
Directions: There are 4 passages in this part. Each of the passages is followed by ,5 questions or unfinished statements. For each of them there are 4 choices marked A, B, C and D. Choose the best one and mark your answer on the ANSWER SHEET with a single line through the center.
Passage One
| In science, a theory is a reasonable explanation of observed events that are related. A theory often involves an imaginary model that helps scientists picture the way an observed event could be produced. A good example of this is found in the kinetic (运动的) molecular theory, in which gases are pictured as being made up of many small particles that are in constant motion. A useful theory, in addition to explaining past observations, helps to predict events that have not as yet been observed. After a theory has been publicized, scientists design experiments to test the theory. If observations confirm the scientists’ predictions, the theory is supported. If observations do not confirm the predictions, the scientists must search further. There may be a fault in the experiment, or the theory may have to be revised or rejected. Science involves imagination and creative thinking as well as collecting information and performing experiments. Facts by themselves are not science. As the mathematician Jules Henri Poincare said: "Science is built with facts just as a house is built with bricks, but a collection of facts cannot be called science anymore than a pile of bricks can be called a house. " Most scientists start an investigation by finding out what other scientists have learned about a particular problem. After known facts have been gathered, the scientist comes to the part of the investigation that requires considerable imagination. Possible solutions to the problem are formulated. These possible solutions are called hypotheses. In a way, any hypothesis is a leap into the unknown. It extends the scientist’s thinking beyond the known facts. The scientist plans experiments, performs calculations, and makes observations to test hypotheses. For without hypotheses, further investigation lacks purpose and direction. When hypotheses are confirmed, they are incorporated into theories. |
In the third paragraph, bricks are mentioned to indicate how ______.
A．science is more than a collection of facts
B．scientific experiments have led to improved technology
C．building a house is like performing experiments
D．mathematicians approach science