28. __ because the sea is full of colorful fish and coral reefs." The phrase "coral reefs" can be defined as __ A. underwater coral structures ; that support marine life B. layers of sand that accumulate on the ocean floor C. seaweeds that grow along the coastline D. land rocks formed by volcanic activity

A. underwater coral structures that support marine life

## Step 1The problem is asking for the definition of the term "coral reefs". The term "coral reefs" is a biological term that refers to underwater structures formed by the accumulation of coral, which is a type of marine organism.## Step 2Coral reefs are known to support a wide variety of marine life, including fish, invertebrates, and algae. They are not related to sand layers, seaweeds, or volcanic rocks.## Step 3Given the options, the correct definition of "coral reefs" is the one that aligns with the biological definition and the role of coral reefs in the marine ecosystem.