Answer:
The correct answer is - option A is continuous variation that follows a geographic continuum.
Step-by-step explanation:
A cline is a slow change in the physical and genetic traits of a population or species across a geographical difference or gradient. If a species present in a very large area, there would be some members live on different environmental condition in comparison to others.
By this gradient members of species show continuous variation that follows a geographic continuum. For, example, In a species of warm-blooded animals have large body size in cooler area than in warmer area.
Thus, the correct answer is - option A is continuous variation that follows a geographic continuum.