如图所示，中子内有一个电荷量为的上夸克和两个电荷量为的下夸克_爱下问搜题

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问题选择题

如图所示，中子内有一个电荷量为的上夸克和两个电荷量为的下夸克，3个夸克都分布在半径为 r 的同一圆周上，则3个夸克在其圆心处产生的电场强度为：

A．　

B．

C．　

D．

答案

A

题目分析: 一个下夸克在圆心处产生的电场强度大小为两个电荷量为的下夸克在圆心处产生的合场强大小为方向沿A→O电荷量为的上夸克在圆心处产生的电场强度大小为向沿A→O，所以3个夸克在其圆心处产生的电场强度大小，方向沿A→O．故选A

完形填空

One day I took a bus with my girlfriend. It was so        that we stood for several stops until a vacant seat was        for her.
Then a pretty girl rushed towards me, saying, "Hi, where are you going?" I was so struck by the stranger that I had a hard time trying to        her. Clearly she had taken me       somebody else. I returned her greeting with politeness,       to give explanation to my girlfriend later.
Noticing my dialogue with somebody else, my girlfriend       her eyes and found she was pretty. She asked jealously, "Who's she?" The pretty girl, quite       of the situation, spoke out first, "Hi, let me        myself. I'm Nancy, used to be       . Very glad to meet you." She behaved very       .
But I was        to search in my memory for someone called Nancy among my neighbors. I was worrying how to explain this to my girlfriend       the pretty girl again turned to me, "Will you give me your cell phone number so that we        keep contacts later?" I had to submit to her       . Then the girl got off the bus at the next stop.
A minute later I got a short        on my phone－from a stranger. My girlfriend       my phone and read the note. It was from the girl, who said, "Just now, two thieves tried to       your pocket. I had to act as an acquaintance to draw your attention. I should have left at the        stop but gave up as I noticed these two thieves also        to leave at the same stop. Because of the       I delayed my departure. Now you' ll understand all I have done to you. Wish you luck."

单项选择题

福建南部的客家土楼住宅各层空间的使用功能分别为( )。

A．底层畜圈、储粮；二层厨房、公共活动；三、四层住房
B．底层厨房、畜圈；一层、三层为住房；顶层储粮
C．底层为祠堂、公共活动、厨房、畜圈；二层以上为住房
D．底层厨房、畜圈、杂用；--层储粮；上两层为住房