人踢球时,如果以球为研究对象,施力物体是 ____ ,受力物体是 ____ .
已知|x+1|+(x﹣y+3)2=0,那么(x+y)2的值是( )
新航路的开辟使世界市场开始形成,最能够说明这一结论的是( )
Jenny couldn't find bike. had to walk to school.