题目内容

位移电流的实质是电场

A. 对
B. 错

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下列说法正确的是

A. 动生电动势是洛仑兹力对导体中自由电荷做功而引起的
B. 因为洛仑兹力对运动电荷始终不做功，所以动生电动势不是由洛伦兹力而产生的
C. 动生电动势的方向可以由右手定则来判定
D. 导体棒切割磁感线产生感应电流，受到的安培力一定与受到的外力大小相等，方向相反

Read the following passage and answer the related questions.A hobby can be almost anything a person likes to do in his sparetime．Hobbyists raise pets, build mode ships, weave baskets, watch birds, hunt animals, climb mountains, raise flowers, fish, ski, skate, and swim．Hobbyists also paint pictures, attend concerts and plays, and perform on musical instruments．They collect everything from books to butterflies, and from shells to stamps．People take up hobbies because these activities offer enjoyment, friendship, knowledge and relaxation．Sometimes they even yield financial profit．Hobbies help people relax after periods of hard work, and provide a balance between work and play．Hobbies also offer interesting activities for persons who have retired．Anyone, rich or poor, old or young, sick or well, can follow a satisfying hobby, regardless of his age, position, or income．Hobbies can help a person’s mental and physical health．Doctors have found that hobbies are valuable in helping patients recover from physical or mental illness．Hobbies give bedridden or wheel-chair patients something to do, and provide interests that keep them from thinking about themselves．Many hospitals treat patients by having them take up interesting hobbies or pastimes．In early times, most people were too busy making a living to have many hobbies．But some persons who had leisure did enjoy hobbies．The ancient Egyptians played games with balls made of wood or pottery．People today have more time than ever before for hobbies．Machines have reduced the amount of time they must spend on their jobs．Hobbies provide variety for workers who do the same monotonous(单调的)tasks all day long．More people are retiring than ever before, and at an earlier age．Those who have developed hobbies never need to worry about what to do with their newly-found leisure hours．Sir William Osler, a famous Canadian doctor, expressed the value hobbies of hobbies by saying．“No man is really happy or safe without a hobby．”1.哪种开头段方法？

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