如图所示，固定在水平桌面上的金属框架cdef，处在竖直向下的匀强磁场中，金属棒ab搁在框架上，可无摩擦滑动，此时adeb构成一个边长为L的正方形，开始时磁感应强度为B0．若从t=0时刻起，磁感应强度逐渐减小，棒以恒定速度v向右做匀速运动时，可使棒中不产生感应电流，则磁感应强度应怎样随时间变化（写出B与t的关系式）？
要使棒不产生感应电流，穿过回路的磁通量应保持不变，则有：
B0L2=BL（L+vt），
解之得：B=B0L L+vt
答：磁感应强度随时间变化的规律为：B=
．B0L L+vt
目前禽流感A/H5N1病毒感染人类的可能途径有（）。
A.禽→人
B.环境→人
C.人→人
D.母亲→胎儿
E.兽→人
陆地撤离应首先选垂直飞机的方向跳离，然后选风上侧躲避，远离飞机至少（）以外。
十进制整数86转换成二进制整数是
A．01011110
B．01010100
C．010100101
D．01010110
In one very long sentence, the introduction to the U. N. Charter expresses the ideals and the common aims of all the people whose governments joined together to form the U. N.
"We, the people of the U. N. , determined to save succeeding generations from the scourge of war which twice in our lifetime has brought untold suffering to mankind, and to reaffirm faith in fundamental rights, in the dignity and worth of the human person, in the equal rights of men and women and of nations, large and small, and to establish conditions under which justice and respect for the obligations arising from treaties and other sources of international law can be maintained, and to promote social progress and better standards of life in larger freedom, and for these ends, to practise tolerance and live together in peace with one another as good neighbours, and to unite our strength to maintain international peace and security, and to ensure, by the acceptance of principles and the institution of methods, that armed force shall not be used, save in the common interest, and to employ international machinery for the promotion of economic and social advancement of all peoples, have resolved to combine our efforts to accomplish these aims."
The name "United Nations" is accredited to U. S. President Franklin D. Roosevelt, and the first group of representatives of member States met and signed a declaration of common intent on New Year’s Day in 1942. Representatives of five powers worked together to draw up proposals, completed at Dumbarton Oaks in 1944. These proposals, modified after deliberation at the conference on International Organization in San Francisco which began in April 1945, were finally agreed on and signed as the U.N. Charter by 50 countries on 26 June 1945. Poland, not represented at the conference, signed the Charter later and was added to the list of original members. It was not until that autumn, however, after the Charter had been ratified by China, France, the U. S. S. R. U. , the U.K. and the U. S. and by a majority of the other participants that the U. N. officially came into existence. The date was 24 October, now universally celebrated as United Nations Day.
The essential functions of the U. N. are to maintain international peace and security, to develop friendly relations among nations, to cooperate internationally in solving international economic, social, cultural and human problems, promoting respect for human rights and fundamental freedoms and to be a centre for co-ordinating the actions of nations on attaining these common ends.
No country takes precedence over another in the U. N. Each member’s rights and obligations are the same. All must contribute to the peaceful settlement of international dispute, and members have pledged to refrain from the threat or use of force against other states.
Under its Charter, the first stated aim of the U.N. was（）
A. to promote social progress
B. to prevent a third world war
C. to revise international laws
D. to maintain international peace
银企对账网银签约时，验印方式选择为（）。
A.支付密码
B.电子验印
C.预留印鉴
D.手工验印
