题干

请根据图中小磁针静止时N极的指向,标出通电螺线管的N极,并在括号内标出电源的“+”、“﹣”极.

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解:由小磁针N极靠近螺线管的右端,所以螺线管的右端为S极,左端为N极,根据安培螺旋定则,螺线管中的电流应由左端流入,所以电源左端为正极,右端为负极;如图所示:

同类题4

根据短文内容,从短文后的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。

      Both men and women are livinglonger these days in industrialized countries.____Ingeneral, they can expect to live six or seven years more than men. One reasonfor this is biological.

      One important biological factor thathelps women live longer is the difference in hormones between men and women.____Between the ages of about 12 and 50,women produce hormones that are involved in fertility(生育能力). These hormones also have a positive effect on the heartand blood flow. In fact, women are less likely to have high blood pressure orto die from heart attacks.

       ____Theyhelp the body defend itself against some kinds of infections. This means thatwomen generally ger sick less often and less seriously than men. The commoncold is a good example: women, on average, get fewer colds than men.____ Scientists are still not exactly sure howinfluence aging, but they believe that they do. Some think that a woman's bodycells have a tendency(向) to age more slowly than a man's. Others think that a man's body cells have a tendency to age more quickly.____

A.However,women, on average, live longer.

B .The biological factorplays an important part.

C. Women are also helped bytheir female genes.

D. The female hormones alsoprotect the body in another way.

E. Recent research seems tosupport both of these possibilities.

F. Therefore, women are morehealthy than men and can live a better life.

G. Hormones are chemicalswhich are produced by the body to control carious body functions.