A.-5 B.-5! C.0 D.-1
解析:f′(x)=(x-1)(x-2)(x-3)(x-4)(x-5)-x[(x-1)(x-2)(x-3)(x-4)(x-5)]′,
∴f′(0)=-1×(-2)×(-3)×(-4)×(-5)=-5!.
答案:B