题目

如图所示，n=10匝的矩形闭合线圈ABCD在匀强磁场中绕垂直于磁场方向OO＇轴匀速转动。转轴OO＇过AC边和BD边的中点。若从图示位置开始计时，穿过线圈的磁通量Φ随时间t的变化关系可以表示为Φ=0.1cos(10πt)（Wb），时间t的单位为s。已知矩形线圈的电阻为10Ω ( 取π=3.14，π2=9.86 ) ，则下列说法中正确的是A．在任意l s时间内，线圈克服安培力所做的功为49.3JB．任意1s时间内，线圈中电流方向改变20次C．电流的有效值为3.14AD．穿过线圈磁通量的最大值为0.1Wb Looking at China's history over the past 60 years，it is apparent that，despite much suffering，the country has achieved huge political，economic and social success，especially during the past three decades.The press center for the celebration of the 60th founding anniversary of new China was officially opened on the morning of September 22. Zha Shouchen，deputy director of the press center introduced that，during the National Day，there would be 3,200 domestic reporters，and more than 1,300 foreign journalists to come to Beijing to make the covering work.The press center provided many services for domestic and foreign reporters，such as issuing the press cards to reporters，accepting the interview application，organizing press conferences and activities of group interviews，providing the means of communication and information services for reporters.And the following was the scene.A grand parade in Beijing on Oct.1，led by the People's Liberation Army and the People's Armed Police Force，showed some of China's latest achievements in defense modernization.About 8,000 military officers，along with tanks and other vehicles，formed a straight line stretching 3 kms.The military parade was followed by a civilian parade featuring six massive performing groups and 36 formations of about 100,000 people.In addition,60 floats(彩车)represented everything from the country's geographic areas to the previous year's Beijing Olympics.Everyday life in China is a parade on a grand scale，with citizens now being able to enjoy things their ancestors did not dare to contemplate 100 years ago，things their grandparents took for luxury 60 years ago，and things their parents did not even know how to attempt 30 years ago.【1】Of the following achievements，which one is NOT listed in Paragraph 1?A. Politics. B. Economy.C. Education. D. Society.【2】Which of the following led the parade according to Paragraph 4?A. The People's Liberation Army.B. The People's Liberation Army and the People's Armed Police Force.C. The People's Police Force and the People's Army.D. The People's Armed Police Force.【3】Which of the following statements is NOT true according to the text?A. The civilian parade is after the military parade.B. There are 60 floats representing everything from the country's geographic areas.C. Everyday life in China is a parade on a grand scale.D. The parade on Oct.1 showed some of China's latest achievements in automotive modernization，such as tanks and other vehicles.【4】What's the subject discussed in the text?A. The celebration of 60th anniversary of the founding of New China.B. The grand parade in the ceremony.C. The defense modernization in China.D. The economic development during recent years.