如图用一个动滑轮把一个重为100N的沙袋从地面提高到9m的脚手架上，所用的力F是60N，则该动滑轮（   ）

小丽用圆规画一个周长是15.7cm的圆，圆规两脚间应量取的距离是（　　）cm．

    Attention！Sunshine Language Learning Centre will set a course and it will teach Pure（纯正的） British English. Maybe you've known some British expressions are quite different from American ones。British people use “autumn” for “fall”, “film” for “movie”. “holiday” for “vocation”, “garden” for “yard”. etc

    There are more typical（典型的）expressions that you may not know. Here are Mr. Bean's examples.

    Are you interested in it? Do you want to learn? You can learn British English well if you put much effort into it. We have some native British English teachers with much experience to help you.

    The course will be open in the coming summer holiday. The price of the course is not very high: ￥500 for one person; ￥900 for two（10% off）; ￥1,200 for three (20% off); for four or more(30% off).

    For further details, call 400-810-2345 or search http://www.BEcourse.com. Come and join us!

一个真分数，如果它的分子和分母同时加上一个非0的自然数，其分数值变大。