I was in the kitchen ____ (help) my mom when you called me
已知平面上两点M(-5,0)和N(5,0),若直线上存在点P使|PM|-|PN|=6,则称该直线为“单曲型直线”,下列直线中是“单曲型直线”的是( )①y=x+1; ②y=2; ③y=43x; ④y=2x+1.