How Do Reservoir Populations Allow Parasites to Persist in Nature

How do reservoir populations allow parasites to persist in nature?

A) Reservoir species transmit the parasite more frequently than host species, so the parasite infects a larger number of individuals.
B) Reservoir species are necessary for reproduction of the parasite.
C) Reservoir species do not die of the parasite and can be a continuous source of the parasite.
D) Without the reservoir species, the parasite could not disperse from one host to another.