如图，两木块A和B被水平力F通过挡板C压在竖直墙上，处于静止状态，则（   ）

选词填空。

excited, skill, may, they, without, but, include, part

    American teenagers(青少年)enjoy doing part-time jobs．They think it's an important____of growing up．They can learn some important____by doing part-time jobs and they can also make some money in this way．
    American teenagers usually begin to do part-time jobs at the age of 14．On weekdays，they____go to work a few hours a week after school．They usually work for longer at weekends．
    In summer,American teenagers are____if they find part—time jobs at camps or swimming pools．These jobs can bring____much fun．
    Some difficult jobs____teaching， nursing and police work．____these jobs can be helpful for their future．When they grow up，the students with work experience are more likely (可能的)to be successful than those____work experience．

某实验小组同学对双氧水制氧气的若干问题进行探究．

若一个多边形的内角和比外角和大360°，则这个多边形的边数为____．

It's important_______ the piano well.