有关洛伦兹力和安培力的描述，正确的是（   ）

给下图标序号。

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如图所示，一个带正电的粒子以一定速度进入匀强磁场中，匀强磁场的方向竖直向下，关于此时带电粒子所受的洛伦兹力的方向，下列说法正确的是（   ）

阅读下面的短文，然后根据短文内容，在每小题所给的四个选项中选出最佳选项。
                                                                                          C
  “How are you?” is a nice question. It's a friendly way that people in the USA greet each other. But “How are you” is also a very unusual question. It's a question that often doesn't need an answer. The person who asks “How are you?” hopes to hear the answer “ Fine”, even if the person's friend isn't fine. The reason is that “How are you?” isn't really a question and “Fine” isn't really an answer. They are simply other ways of saying “Hello” or “Hi”.
    Sometimes, people also don't say exactly what they mean. For example, when someone asks “Do you agree?” the other person might think, “No, I disagree. I think you’re wrong…” But it isn't very polite to disagree so strongly, so the other person might say “I'm not sure.” It's a nicer way to say that you don't agree with someone.
    People also don't say exactly what they are thinking when they finish talking with other people. For example, may talks over the phone finish when one person says “I've to go now.” Often, the person who wants to hang up gives an excuse “Someone's at the door.” “Something is burning on the stove.” The excuses might be real, or not. Perhaps the person who wants to hang up simple doesn't want to talk any more, but it isn't polite to say that. The excuse is more polite, and it doesn't hurt the other person.
    Whether they are greeting each other, talking about an idea, or finishing a talk, people don't say exactly that they are thinking. It's an important way that people try to be nice to each other, and it's part of the rule of the game of language.

如图所示，平行板电容器的电容为C，带电荷量为Q，板间距离为d，今在两板的中点处放一电荷q，则它所受电场力的大小为（   ）