If biologists show that both p and q are not changing over a period of time, the statement that must be true is:
C. There is no migration in the population.
The Hardy-Weinberg equation assumes that certain conditions are met for a population to be in genetic equilibrium, one of which is the absence of migration. Migration can introduce new alleles into a population or remove existing alleles, which would disrupt the equilibrium and cause changes in allele frequencies (p and q). Therefore, if p and q are not changing, it suggests that there is no migration occurring in the population.