下列从左到右的变形属于因式分解的是()
A.x2-2xy+y2=x(x-2y)+y2
B.x2-16y2=(x+8y)(x-8y)
C.x2+xy+y2=(x+y)2
D.x4y4-1=(x2y2+1)(xy+1)(xy-1)