Which of the following would be the best example of adaptive radiation, where a species evolves into different forms and fills different niches?

a. A raccoon born in a woodland near a city wanders into the city and learns to find food in an urban environment.
b. A species of plant grows on a mountain at high elevation that is very similar genetically to another species growing at lower elevations on the mountain.
c. A species of beetle moves into a new area and out competes the resident beetle species, driving the resident species to extinction.
d. Plants living in dry areas all over the world produce bad-tasting resins in their leaves to keep animals from eating them.