设﹣2<a<7,1<b<2,求a+b,a﹣b,ab 的范围.
下列对生活中物理量的估测接近事实的是( )
My father often does many kinds of sports, such as ____ (playing/to play) football and swimming.
中学生王佳在去年“十一”黄金周外出旅游时,发现一位外国游人向插有“军事禁区”标志的山林内录像。王佳随后拨打“110”报警,使这名外国游人受到有关部门的依法查处。王佳同学的行为( )