题干

已知雨滴在空中竖直下落时所受空气阻力与速度的平方成正比,且不同质量的雨滴所受空气阻力与速度大小的二次方的比值相同.现有两滴质量分别为m1和m2的雨滴从空中竖直下落,在落到地面之前都已做匀速直线运动,那么在两滴雨滴落地之前做匀速直线运动的过程中,其重力的功率之比为(   )

A:m1:m2

B:m1m2

C:m2m1

D:m13m23

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D

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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.