已知金星绕太阳公转的周期小于1年，则可判定（） ①金星到太_爱下问搜题

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问题选择题

已知金星绕太阳公转的周期小于1年，则可判定（　　）

①金星到太阳的距离小于地球到太阳的距离

②金星的质量大于地球的质量

③金星的密度大于地球的密度

④金星的向心加速度大于地球的向心加速度．

A．①③

B．②③

C．①④

D．②④

答案

根据万有引力提供向心力，G

Mm

r2

=m(

2π

T

)2r=ma知，T=2π

r3

GM

，a=

GM

r2

，知周期小，轨道半径小，向心加速度大．因为金星的周期小于地球公转周期，则金星到太阳的距离小于地球到太阳的距离．金星的向心加速度大于地球的向心加速度．环绕天体的质量无法求出，也无法比较，所以密度也无法比较．故①④正确，②③错误．

故选C．

选择题

* * 给我们最深刻的教训是 [ ]

A．要防止个人崇拜

B．要正确认识社会主义初级阶段阶级斗争问题

C．要健全社会主义民主与法制

D．要警惕党内的反革命集团

完形填空

Once there was a very brilliant, creative and educated man. He gained much 36  while traveling throughout the world. 37 , he lost his legs and left arm in a tragic accident, leaving only a finger and thumb on his right hand. He became so depressed(沮丧的）that he was afraid he would spend his life 38  and would no longer be able to use his life in a(n)   39  way.
One day, he remembered how he had always loved getting 40 . He realized that he still had partial   41 of his right hand and could write with 42 . Then, he had an idea. “Why not write to other people who need encouragement?”
He 43 where he could find those who could be encouraged if they read his letters. He thought of people in 44 . Many of them had hope of regaining their 45 . Others would keep feeling depressed and remain put away for the rest of their lives. He decided that he must try to 46 them. So he wrote to a prison ministry about sending letters to the prisoners. The prison minister replied that writing to the prisoners would be 47 . However, it would be against prison rules for the prisoners to write back.
48 with the intention, the man began sending 49 messages of God’s love, hope, strength, and encouragement. He wrote twice a week, testing his strength and ability to the limit. He poured his heart and soul 50 his words, 51  his experience, sense of humor, optimism, and faith.
It was difficult to write those letters, especially without hope of any  52 . Frequently, he felt discouraged, wondering if anyone 53 read his letters. However, this was his 54   chance，so he determined to continue.
At last, he received a letter from the prison officer, which said, “Please write on the best paper you can afford. Your letters are passed from cell (牢房) to cell until they almost fall to   55 !”
We all have unique experiences, abilities and talents. We can discover ways to reach others in need of encouragement and strength.

A．Unfortunately	B．Fortunately
C．Surprisingly	D．Unbelievably

C．comfortable

A．keep in touch with	B．get in touch with
C．defend	D．know