Answer:
c. are
Explanation:
you wouldn't say the mountains of colorado am your vacation, since am is used to describe how you are or what you are. You wouldn't use be either becuase you use be to talk about feelings and states. Now, what about is. Is is very similar to are, and it is used in the same way, but are is the plural version of is. And, since there are many mountains, not just one, you would use are.
