19．The twentieth century saw greater changes than any century before．Changes for the better，changes for the worse，changes that brought a lot of benefits to human beings，changes that put man in danger．Many things caused the changes，but，in my opinion，the most important was the progress in science．
Scientific research in physics and biology has vastly broadened our views．It has given us a deeper knowledge of the structure of matter and of the universe．It has brought us a better understanding of the nature of life and of its continuous development．Technology in the application of science has made big advances that have benefited us in nearly every part of life．
The continuation of such activities in the twenty-first century will result in even greater advantages to human beings； in pure science-a wider and deeper knowledge in all fields of learning； in applied science-a more reasonable sharing of material benefits，and better protection of the environment．
Sadly，however，there is another side to the picture．The creativity of science has been employed in doing damage to mankind．The application of science and technology to the development and production of weapons of mass destruction has created a real danger to the continued existence of the human race on this planet．We have seen this happen in the case of nuclear weapons．Although their actual use has so far occurred only in the Second World War，the number of nuclear weapons that were produced and made ready for use was so large that if the weapons had actually been used，the result could have been the ruin of the human race，as well as of many kinds of animals．
William Shakespeare said，"The web of our life is of a mingled yarn，good and ill together．"
The above brief review the application of only one part of human activities-science seems to prove what Shakespeare said．But does it have to be so？Must the ill always go together with the good？Are we biologically programmed for war？
21．Which of the following best shows the structure of the passage？A
（①=Paragraph 1，②=Paragraph 2，③=Paragraph 3，④=Paragraph 4，⑤=Paragraph 5）
22．From the fourth paragraph，we can infer thatD．
A．a(chǎn) great many nuclear weapons were actually used for war
B．a(chǎn) large number of nuclear weapons should have been used for war
C．the author is doubtful about the ruin of human beings by nuclear war
D．the author is anxious about the huge number of nuclear weapons on the earth
23．What do you think the author is most likely to suggest if he continues to write？D
A．Further application of science to war．
B．More reading of William Shakespeare．
C．Proper use of science in the new century．
D．Effective ways to separate the good from the ill．
