4题20分哦 因式分解
1-3(x-y)+3(x-y)^2-(x-y)^3a^2+b^2+4a-4b-2ab+4(x+y)^2+
(x+m)^2-(m+n)^2-(y+n)^2a^2(b^2-c^2)-c^2(b-c)(a+b)