如图所示,在一水平长木板上放一木块P,缓慢抬起木板的右端,木块P和木板始终相对静止,则( )
His grandfather ____ ____ a lot of hardships during the war.
把下面的有理数填入它属于的集合内(将各数用逗号分开)
3.14,0,﹣2,80,﹣2.1,227,﹣130,﹣35,
负数集合{____ …};
整数集合{____ …}.