The answer is D.
Now, (x+y)3−(x3+y3)=(x+y)3–(x+y)(x2−xy+y2)
[Using identity, a3+b3=(a+b)(a2−ab+b2)]
=(x+y)[(x+y)2–(x2–xy+y2)]
=(x+y)(x2+y2+2xy−x2+xy−y2)
[Using identity, (a+b)2=a2+b2+2ab)]
=(x+y)(3xy)
Hence, one of the factor of given polynomial is 3xy.