A.0 B.24 C.-24 D.-120
解析: f'(x)=(x-1)'(x-2)(x-3)(x-4)(x-5)+(x-1)[(x-2)(x-3)(x-4)(x-5)]',
所以f'(1)=(1-2)(1-3)(1-4)(1-5)=24.
答案:B