已知a和c是常数，下面哪个选项是幂律分布的正确形式？

A、f(k) = ak⌃-c
(a大于0，c大于0);

B、f(k) = ac⌃-k
(a大于0，c大于0);

C、f(k) = ak⌃-c
(a大于0，c小于0);

D、f(k) = ac⌃-k
(a大于0，c小于0)