题干

如图所示,在竖直面内有一以O点为圆心的圆,AB、CD分别为这个圆沿竖直和水平方向的直径,该圆处于静电场中.将带负电荷的小球从O点以相同的动能分别沿竖直平面向不同方向射出,小球会沿圆所在平面运动并经过圆周上不同的点.已知小球从O点分别到A、B两点的过程中电场力对它做的功相同,小球到达D点时的电势能大于它在圆周上其他各点时的电势能.若小球只受重力和电场力的作用,则下列说法中正确的是(   )

A:小球到达B点时的机械能与它在圆周上其他各点相比较最小

B:小球到达A点时的电势能和重力势能之和与它在圆周上其他各点相比较最小

C:此电场可能是位于C点的正点电荷形成的

D:小球到达B点时的动能等于到达点A时的动能

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C

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    Persuasion is the art of convincing someone to agree with you. According to the ancient Greeks, there are three basic tools of persuasion : ethos, pathos, and logos.

    Ethos is a speaker's way of convincing the audience that she is trustworthy, honest and reliable. One common way a speaker can develop ethos is by explaining how much experience or education she has in the field. After all, you're more likely to listen to advise about how to take care of your teeth from a dentist than a fireman. A speaker can also create ethos by convincing the audience that she is a good person. If an audience cannot trust you, you will not be able to persuade them.

    Pathos is a speaker's way of connecting with an audience's emotions. For example, a politician who is trying to convince an audience to vote for him might say that he alone can save the country from a terrible war. These words are intended to fill the audience with fear, thus making them support him. Similarly, an animal charity might show an audience pictures of injured dogs and cats, to make the viewers feel pity. If the audience feels bad for the animals, they will be more likely to donate money.

    Logos is the use of facts, statistics, or other evidence to support your argument. An audience will be more likely to believe you if you have convincing data to back up your claims. Presenting this evidence is much more persuasive than simply saying “believe me”.

    Although ethos, pathos, and logos all have their strengths, they are often most effective when used together. Indeed, most speakers use a combination of ethos, pathos, and logos to persuade their audiences. So, the next time you listen to a speech, watch a commercial, or listen to a friend try to convince you to lend him some money, be on the lookout for these ancient Greek tools of persuasion.