Which Statement About the Snail-Trematode System Studied by Dybdahl and Lively

Which statement about the snail-trematode system studied by Dybdahl and Lively is false?

A) Parasites infected snails from their home lake less effectively than those from other lakes.
B) The most common genotype of snail often varied from year to year.
C) The parasites can castrate male snails.
D) The type of parasite varied from year to year.