You Learn That Many Plants Are Chemically Defended and That

You learn that many plants are chemically defended and that herbivorous predators have developed resistance to many of these plant defenses.However,it appears that plants have responded to herbivore resistance by producing more chemical defenses,which in turn deters some herbivores.Evidently,this process has occurred many times over the last millions of years.This is an example of:

A) Reciprocal transplantation
B) Co-evolution
C) Allopatric speciation
D) Mutualism