A:
B:
C:
D:
如图,直线l与半径为3的⊙O相切于点A,P是⊙O上的一个动点(不与点A重合),过点P作PB⊥l,垂足为B,连结PA,设PA=m,PB=n,则m﹣n的最大值是( )
One way ____ (solve) this problem is ____ (plan) your time more carefully.