The northern copperhead is Agkistrodon contortrix contortrix, the southern copperhead is Agkistrodon contortrix mokasen, and the cottonmouth is Agkistrodon piscivorous. Therefore,

A. all are subspecies of Agkistrodon.

B. they are three distinct species.

C. the copperheads are subspecies and the cottonmouth is a separate species.

D. they are all the same species.

Therefore "the copperheads are subspecies and the cottonmouth is a separate species".

Answer: Option C

Explanation:

The higher classification is "copperhead" for both the subspecies Agkistrodon contortrix contortrix and Agkistrodon contortrix mokasen. As the name itself consist species name "A. contortrix", both are belonging from "Viperidae" family, "Crotalinae" subfamily and venomous pit viper subspecies.

These are generally silent snakes as they show lazy and motionless behavior when encountered but on agitating sufficiently they become protectively aggressive and they are species of eastern North America. While Agkistrodon piscivorous are separate species with higher classification as "Cottonmouth" and name carry species name "A. piscivorus". It is indigenous to southeastern United States and belongs to same family as copperhead.