题干

如图所示的实验装置,是用来研究____(选填“电流磁效应”、“电磁感应现象”或“磁场对通电导线的作用”)的.实验中把导线ab放在磁场里,接通电源,让电流通过导线ab,会观察到导线向右运动;如果把电源正、负极对调后接入电路,会观察到导线ab向____(选填“左”或“右”)运动;如果不对调电源正、负极,但把蹄形磁体上下磁极调换一下,会观察到导线ab向____(选填“左”或“右”)运动;如果把电源正、负极对调,同时把蹄形磁体上下磁极也调换则会观察到导线ab向____(选填“左”或“右”)运动.

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磁场对电流的作用,左,左,右

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    Six years ago, I walked into a local animal shelter on a cold, rainy day.1my house was already full of cats and dogs, I still couldn't 2an occasional visit to the shelter. This time as I was walking down the row of pens(畜栏) full of barking dogs, I3a small boy looking into one of them.

    He had a malnourished(营养不良的)looking body and a4face with a big nose5out of the middle of it. He was looking at a small golden dog. Its ribs(肋骨)were showing and its thin tail was folded between its legs. It wasn't begging for6like the other puppies7was hiding in the corner instead. The boy looked up at me with8eyes and asked what was wrong with it. “It was probably abused and9 ” I said. “That is why it is so 10 ”

    The boy 11turned to an old lady and said, “ Grandma, I want this one.” The old woman smiled and walked to the front desk to fill out the 12forms. I followed her and asked 13the boy. She told me that he'd had a 14start in life, too. She had just gotten custody(监护权) of him15the state had taken him from his parents. She hoped getting a dog would make his life 16for him. I looked back at him, holding his scared puppy, and said a prayer for them both.

    It was yesterday that I was driving down the road enjoying a gloriously sunny, spring day. Then in a green front yard I saw the boy. His 17body was tall and strong. His nose no longer 18big but fit well into his smiling face. He was throwing a ball to a healthy, happy dog shining golden hair. His little act of love and 19had indeed gone a long way. It had saved a dog's life, 20his own heart, and given this middle-aged man fresh hope for the whole world.