问题 选择题

要使感应电流的方向相反,可采用的措施有(  )

A.把磁场方向和切割磁感线的导体的运动方向都反过来

B.保持导体切割磁感线运动的方向不变,再把磁场方向反过来

C.将磁场方向和切割磁感线的导体的运动方向都改变

D.以上方法都可以

答案

A、把磁场方向和切割磁感线的导体的运动方向都反过来,感应电流方向不变,故A错误;

B、保持导体切割磁感线运动的方向不变,再把磁场方向反过来,感应电流方向变化,故B正确;

C、将磁场方向和切割磁感线的导体的运动方向都改变,感应电流方向不变,故C错误;

D、由于AB错误,所以D错误;

故选B.

多项选择题
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Teddy Bears have been a very popular children’s toy for many years. Most adults can remember their first stuffed(填充玩具)bear, and over the decades these toys have become nearly a symbol of their childhood. However, children are not the only ones with whom these toys have become popular, as many adults make it a habit to collect these toys as well.

The Teddy Bear first became popular during the early 20th century and was associated with then President Theodore Roosevelt. The story can date back to a hunting trip that President Roosevelt had taken where he was invited to be the one to shoot a black bear that had been tied to a tree. Being a crazy outdoors lover and hunter, Roosevelt refused to kill the animal because he believed that shooting the helpless bear was unsportsmanlike and wrong. This story quickly spread through newspapers across the country, and in the end inspired the introduction of a stuffed toy called “Teddy’s bear”.

These toys became popular soon after first introduced, and within ten years, they were being produced by dozens of companies around the world. Within a generation, these stuffed bears were “the” toy to have, and have always been within children’s toy boxes ever since.

They are most often mass-produced in factories in order to keep up with the high demand.  However, there are still companies that take great pride in their handmade designs; and while handmade teddy bears are often preferred, they are also generally more expensive than their mass-produced ones.

Today, these bears and other similar toys generate well over a billion dollars a year in profits for the companies that make them. Walk through just about any toy store in America and you will find dozens of different teddy bears lining the shelves.

小题1:According to the passage, we can know President Roosevelt ______.

A.didn’t like hunting

B.enjoy being special

C.was not brave enough

D.was fair and respectable小题2:Compared with mass-produced teddy bears, the handmade ones ______.

A.don’t sell well

B.are of high quality

C.are more expensive

D.are preferred by adults小题3:From the last paragraph, the writer intends to show ______.

A.teddy bears are very popular

B.toys are loved by many companies

C.producing toys can earn more money

D.teddy bears are also enjoyed by adults小题4:What is the passage mainly about?

A.History of the Teddy Bear.

B.A popular toy — Teddy Bear.

C.Who made the first toy bear?

D.Profits Teddy Bear have made.