A:x2+y2-2x+4y=0
B:x2+y2+2x+4y=0
C:x2+y2+2x-4y=0
D:x2+y2-2x-4y=0
( )
已知: f(x)=2x-2,x≤2log2(x-1),x>2则f(f(5))等于( )