A:included
B:contained
C:kept
D:owned
____ ____ Jack feel worried?
如图所示,纸片不会掉下来的原因是( )
如图所示水平面上一个静止的小车上有一弯杆,其下端固定一个小球,小球的受力示意图正确的是( )
一个不透明的袋子中装有2个红球、3个白球,每个球除颜色外都相同.从中任意摸出3个球,下列事件为必然事件的是( )
They ________ carefully, but they didn't ________ anything.