Question

Survival of at least a few members of a population after a major environmental change is most dependent on

Answer 1

Survival of at least a few members of a population after a major environmental change is most dependent on 3) variations in many different traits in many individuals in the population.
Variation is important for a species which wants to survive huge changes in the environment. If they cannot adapt to their new surroundings, they won't be able to survive. This is where variation comes in - it enables a species to develop new techniques and traits necessary for survival.