Answer:
The author's purpose in mentioning coral reefs in the article is:
D) to explain how climate change is damaging the delicate ecosystem in coral reefs.
Step-by-step explanation:
The Newsela article "Climate Change in Hawaii and U.S. Tropical Islands" discusses how climate change is affecting islands controlled by the U.S., such as Puerto Rico and the Hawaiian islands. In the last section of the article, the author mentions coral reefs in order to show how this important ecosystem is being threatened and damaged by change in climate. According to the article, coral reefs protect shore line during storms and are home to different kinds of marine life. Due to climate change - warmer sea temperatures, for instance - reefs are shrinking and dying. That will have a great and unfortunate impact on tourism, for example.