Step-by-step explanation:
The correct response is: Changes in the environment can act only on existing variations in a population.
This means that when the environment changes, it can act on the existing variations present in a population, causing certain traits to become more advantageous or disadvantageous for survival and reproduction. This can lead to natural selection and the evolution of the population over time, as the individuals with the most beneficial traits are more likely to survive and pass on their genes to their offspring.