题干

小明用如图所示的电路.探究影响金属丝电阻大小的因素.他手边除了有电路中的器材外.还有一根金属丝,则(   )

A:只能探究电阻与金属丝长度的关系

B:只能探究电阻与金属丝横截面积的关系

C:电阻与金属丝长度、横截面积的关系都能探究

D:电阻与金属丝长度、横截面积的关系都不能探究

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答案(点此获取答案解析)

C

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    Tom Costello was once afraid of homeless Americans. “I was so afraid that if I saw a homeless person walking down the street, I'd cross the street,” he said.

    That changed seven years ago after his wife, Nancy, a volunteer at a homeless shelter, persuaded him to help with a holiday dinner for shelter residents. Tom remembered going to a store and buying socks for the residents. He knew many of them were in need of clothing.

    At the shelter, Tom said, he dropped a pair of socks into a bag for a woman. She asked him if she could have socks for a friend who wasn't with her that day. He gave her another pair. “She started to cry and told me that nobody had ever given her socks before,” Tom said, “Then she reached out and gave me a hug.” That experience at the shelter helped Tom end his fear of the homeless.

    It also led him to set up a group called “The Joy of Sox.”, which borrows from a name of a popular book. The group collects socks from donors and gives them mostly to shelters in the area where Tom and Nancy live. It has been expanding its reach and provides socks to homeless shelters in 21 states and other three countries now.

    Why socks? Tom explains that some Americans give food, coats and other clothing to shelters. But donating socks is not something most people think about. And, he said, socks are very helpful at keeping people warm, especially in cold weather. A man named Kiwi,who has lived in homeless shelters, said most of the time he could find enough food through shelters and soup kitchens. But socks were much more difficult to get, he noted.