Which would stop Hardy-Weinberg equilibrium from happening?

A. There is no immigration into the ecosystem.

B. The organisms choose mates completely randomly.

C. Some individuals produce more offspring than others.

D. Each allele gives an equal chance for survival.

C. The Hardy-Weinberg equilibrium will effectively stop once some individuals produce more offspring than others. Note that this is a principle that involves genotype frequencies in a certain population, and genotype frequencies come from producing genetics; not immigration, choosing mates and survival.