Final answer:
A fan-shaped coral underwater that looks like a tree leaf would provide a clear visual representation of a type of coral, helping to understand the physical appearance and structure of coral reefs.
Step-by-step explanation:
The visual aid of a fan-shaped coral underwater that looks like a tree leaf would help visualize the information in the article by providing a clear visual representation of a type of coral. This visual aid would assist in understanding the physical appearance and structure of coral reefs. It would also help in visualizing how corals build on each other over time to form large structures.