问题
不定项选择
甲、乙两个物体都做匀速圆周运动，其质量之比为1:2，转动半径之比为1：2，在相同的时间里甲转过60°，乙转过45°，则 它们的向心力之比为[ ]
A.1:4
B.2:3
C.4:9
D.9: 16
答案
答案：C
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甲、乙两个物体都做匀速圆周运动，其质量之比为1:2，转动半径之比为1：2，在相同的时间里甲转过60°，乙转过45°，则 它们的向心力之比为[ ]
A.1:4
B.2:3
C.4:9
D.9: 16
答案：C
“I can’t believe what I’m hearing! ”I thought to myself. Jeff was the last candidate（候选人）for president of Student Union. I really thought I should be chosen. Later that day, I happened to pass Jeff in the dining room. I offered a polite “Congratulations” and walked to my usual table. To my , Jeff came to me and put his plate beside mine. “I’m, er-I’m just wondering if you would consider coming to work on my team, ”he said nervously. “You are really and you would be a great partner.” “I don’t think so,” I replied, feeling unsure. “Well, you change your mind, you can tell me tomorrow. ”He said before moving to another table. All that night, I thought about the from Jeff. Maybe being a part of the election process（选举过程）would give me a chance to make important changes at our school. I decided to Jeff. of all, I began to create a catchy advertisement. Within a few days, we a poster with Jeff’s showing him in a number of activities. No one could walk through any hallway passing Jeff’s smiling face. My next step was to what new activities students would like to have at our school. Many of them wanted a chess club and a volleyball team. With the information I had collected, Jeff met with the headmaster. The headmaster agreed to add we want to our school program. With my help, Jeff and our ideas were well received at school. An eighth grader said, “ will be exciting to have Jeff as president.” these words made my heart filled with pride. I had wanted to become president of Student Union to make a difference. Now I achieved that. Jeff became the most popular candidate and I was a large part of his . The fact that it has made a in other people’s lives is the real prize. What a great feeling!
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