—You're right.I decide to________
A:take it down
B:find it out
C:turn it off
D:give it up
--- What about playing ______football after school?
--- I'm afraid I can't. I have to practice playing ______ piano,
____ ____your cousin____ ____ last year?
如图所示,横截面为直角三角形的斜劈A,底面靠在粗糙的竖直墙面上,力F通过球心水平作用在光滑球B上,系统处于静止状态.当力F增大时,系统还保持静止,则下列说法正确的是( )