Which of the following statements is an accurate combination of postulates 1 and 2 of natural selection?

heritable variation exists for traits among individuals in a population.
drug resistance exists among all individuals in a population.
heritable variation does not exist among individuals in a population.
environmental variation exists for traits among individuals in a population.

Heritable variation exists for traits among individuals in a population.

Explanation:

According to Darwin's theory of evolution, natural selection is the main evolutionary mechanism. Darwin explains that organisms that have heritable traits that help them survive and reproduce, will be favorable by natural selection. Those favorable traits will enable organism to better adapt to their environment and to pass more genes on to the next generation (offspring).

Organisms adapt to their environment by changing their behavior, structural traits or physiology as a response to environmental change, so that they become well suited to it.

substitution is the answer in this case