—Didn’t you see the ______, sir? Smoking is not allowed here!
A:sign
B:signal
C:word
D:mark
关于飞机的升力,以下说法正确是( )
(Ⅰ)写出曲线C的直角坐标方程和直线l的普通方程.
(Ⅱ)若P(3, 5 ),直线l与曲线C相交于M,N两点,求|PM|+|PN|的值.