Final answer:
The process by which populations change as individuals best suited to their environment survive and reproduce is known as Natural selection (D). It is the driving force behind evolution in populations and is illustrated by examples like the beak size of Darwin's finches.
Step-by-step explanation:
The term that best matches the definition ‘A process by which populations change because individuals that are best suited for their environment are better able to survive and reproduce’ is D) Natural selection. Natural selection is the mechanism behind evolution where individuals with advantageous traits are more likely to survive and have more offspring. Over time, these traits become more common in the population. This is evident in examples like the beak size changes in Darwin's finches, which varied with the availability of seeds, thus allowing those finches with the most suitable beak sizes to survive and pass on their genes.
Adaptation refers to the outcome of natural selection where organisms develop traits that increase their fitness in a particular environment. However, it is natural selection that describes the process itself by which these advantageous traits become more frequent in a population due to differential survival and reproduction.