题干

如图所示,有一质量不计的长木板,左端可绕O点转动,在它的右端放一重为G的物块,并用一竖直向上的力F拉着当物块向左匀速运动时,木板始终在水平位置保持静止,在此过程中,拉力F(    )

A:变小

B:变大

C:不变

D:先变大后变小

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答案(点此获取答案解析)

A

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阅读理解

    When Abraham Lincoln was young, he worked in a store. One day a woman came into the store and bought some things. They added up to two dollars and six and a quarter cents.

    The bill was paid, and the woman was satisfied. But the young storekeeper, not feeling quite sure about his calculations(计算), added up the things again. To his surprise, he found that it should have been but two dollars.

    “I've made her pay six and a quarter cents more,” said young Abe, upset.

    It was an unimportant thing, and many salespersons would forget it, but Abe was too careful for that.

    The money must be paid back, he decided.

    At night, he closed the store and walked to the home of his customer. He explained the matter, paid over the six and a quarter cents, and returned satisfied.

    Here is another story of young Lincoln's strict honesty. A woman entered the store and asked for half a pound of tea. The young man weighed it out. This was the last sale of the day.

    The next morning, when beginning his duties, Abe discovered a four-ounce weight on the scales(磅砰). It flashed upon him at once that he had used this in the sale last night, and so, of course, given his customer short weight. Many people would not have been much worried by this discovery. But Abe weighed out four ounces of the tea, shut up the store, and carried it to the customer. I think that the name, so often given in late times to President Lincoln, of “Honest Old Abe", was well deserved(应得的).