有两颗绕地球运行的人造地球卫星，它们的质量之比是m1：m2=1：2，它们运行线速度的大小之比是v1：v2=1：2，那么下列说法错误的是（ ）
A．它们运行的周期之比是T1：T2=8：1
B．它们的轨道半径之比是r1：r2=4：1
C．它们的向心力大小之比是F1：F2=1：32
D．它们的向心加速度大小之比是a1：a2=16：1
A、G
=mMm r2
，v=v2 r
．它们运行线速度的大小之比是v1：v2=1：2，则轨道半径比r1：r2=4：1．而T=GM r
，所以周期比T1：T2=8：1．故A、B正确．2πr v
C、G
=ma，a=Mm r2
，轨道半径比为r1：r2=4：1，所以向心加速度比a1：a2=1：16．向心力F=ma，质量之比是m1：m2=1：2，所以向心力之比F1：F2=1：32．故C正确，D错误．GM r2
本题选错误的，故选D．
阅读下面短文，掌握其大意，然后从36—55各题所给的四个选项（A、B、C和D）中，选出最佳选项。 I am a mother of three and have recently completed my college degree. My teacher’s last 36 of the term was called “ Smile”. I am a very friendly person and always 37 at everyone. So I thought this would be very 38 . Soon after we were given the project, my 39 went out to McDonald’s. We were waiting to be 40 , when all of a sudden everyone around us began to 41 , and even my husband did. There standing behind me were two homeless men 42 . As I looked down at the short gentleman with 43 eyes, he said, “ Good day.” The second man stood behind his friend. I 44 the second man was mentally challenged（智障）and the blue-eyed gentleman was his helper. The young 45 at the counter asked him what they wanted. He said, “ Coffee is all ,Miss.” Because that was all they could 46 . I smiled and asked the young lady to give me two more breakfast meals on a 47tray（托盘）. I then said to the men, “ I did not do this for you. God is here 48 through me to give you hope.” When I joined my husband, he smiled at me, saying, “That is 49 God gave you to me, Honey, to give me hope.” I returned to 50 with this story in hand. I 51 “my project” and the teacher read it. Then she looked up at me and said, “ Can I 52 this with the class?” I slowly 53 and she began to read and that was when I knew that we, as human beings, share this to help people and to be 54. In my own way I had 55 the people at McDonald’s, my husband, sons, teacher, and every person that shared the classroom on the last night I spent as a college student.
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