Which of the Following Postulates Makes Up Darwin's Theory of Adaptation

Which of the following postulates makes up Darwin's theory of adaptation?

A) The total resources in a given environment tends to expand as the number of individuals using those resources increases.
B) Only noninherited variation has a long-term impact on evolutionary change.
C) Regardless of variation in parents, genetic mixing makes offspring very similar to each other across a species.
D) Individuals vary in ways that sometimes affect survival or reproduction.