Infection with parasites such as Clonorchis sinensis can occasionally be found in new immigrants to the United States.  However, the primary reason these infections do not become established in the U.S. is _____.

(a) All immigrant centers have indoor toilets
(b) Immigrants are given prescriptions for antihelminthics
(c) The appropriate snail intermediate host is not present in the U. S.
(d) Winter temperatures in the U.S. are too cold for its survival