A group of ants escaped from a picnic basket carried to the top of a mountain and thrived in this area where there were no other ants. Many years later descendants of these ants crawled into a picnic basket on the mountain and traveled back to the valley from which their ancestors had come. Which of these observations would cause you to conclude that the ants on top of the mountain had become a different species from those in the valley?
A) The mountain ants and valley ants were different colors.
B) The mountain ants and valley ants were different sizes.
C) The mountain ants ate different food than the valley ants.
D) The mountain ants could not mate with the valley ants