Correct Option (a)
Australia
The Great Barrier Reef, located in the Coral Sea off the northeastern coast of Australia, is the world's largest coral reef system. It stretches over 2,300 km and encompasses an area of approximately 344,400 square kilometers. Comprising thousands of individual reefs and islands, it supports an extraordinary diversity of marine life and is recognized as a UNESCO World Heritage Site.
Incorrect Options
Cuba (b) and the Philippines (d) possess significant coral reef formations; however, these are not as extensive or continuous as the Great Barrier Reef. Ghana (c), situated on the West African coast, does not host major coral reef systems of global significance.