Answer: A. Cool
Explanation:
The diagram shows that moving from the left to the right indicates a lower temperature and the arrow is pointing to stars to the right which means that they are cool in comparison to those on the left.
Red stars like the one being pointed to are the cooler stars with temperatures of less than 6,000 Kelvin as opposed to blue stars which are very much hotter and go above 10,000 Kelvin.
