题目

Forgetful Nick After school on Friday, when Nick got home, he saw Grandpa’s car! Nick smiled and walked quickly up the front sidewalk. He reached the door and said hello to Grandpa. Then Mom called from the kitchen. “Put away your schoolbag first.” Nick’s smile vanished(消失). “Oh, no,” he said, “I forgot to bring my schoolbag home.” Mom was angry. “Nick, you forgot your schoolbag again! You need to be more careful!” Grandpa turned to Nick and winked(眨眼), “I’m afraid you inherited(遗传) your forgetfulness from me, Nick. Your grandma used to call me 宇宙中，两颗靠得比较近的恒星，只受到彼此之间的万有引力作用互相绕转，称之为双星系统．在浩瀚的银河系中，多数恒星都是双星系统．设某双星系统A、B绕其连线上的O点做匀速圆周运动，如图所示．若AO＞OB，则（ ）A. 星球A的质量一定大于B的质量B. 星球A的线速度一定大于B的线速度C. 双星间距离一定，双星的质量越大，其转动周期越大D. 双星的质量一定，双星之间的距离越大，其转动周期越大