题干

一带负电的点电荷仅在电场力作用下由a点运动到b点的v-t图象如图所示,其中tatb是电荷运动到电场中ab两点的时刻.下列说法正确的是

A:该电荷由a点运动到b点,电场力做负功

B: a点处的电场线比b点处的电场线密

C: ab两点电势的关系为<

D:该电荷一定做曲线运动

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C

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    After my brother died in an accident, my mother was very sad. I was only 4 years old at the time, but I still understood the 1 in my mom's attitude toward safety.2, everything around us was potentially 3.

    I grew up with a lot of 4 and rules that were meant to 5 me. For example, I was not 6 to walk home from school by myself, even though everyone I knew already did. I couldn't 7 evening parties or go to summer camp,8 what if something happened to me?

    As I got older, the list of things to 9 got longer. I became a natural 10. I was concerned about things like getting cancer, losing my wallet, being caught in car accidents and earthquakes —11 big and small, real and 12.The funny part is that you'd never know it by looking at my life, because I'm constantly 13 myself to do the things that frighten or worry me. In fact, I've developed a 14 for myself: If it scares me, then I have to do it 15 once. I've done lots of things that would have 16 my mom: I've ridden a motorcycle, I've traveled alone, and I've performed stand-up comedy.

    Courage isn't a natural attribute (品质) of human beings. I believe that we have to practice being courageous. The more 17 I do things that scare me or that make me 18, the more I realize that I can do a lot more than I originally thought I could do.

    Even though I inherited (经遗传获得) my mother's cautious19, I've also come to believe that fear can be a good thing, if we 20 it. Believing that has made my world a less scary place.