Diego Garcia is an atoll located in the Indian Ocean, which is the correct answer. This strategically vital island is part of the British Indian Ocean Territory and is situated south of the equator, roughly halfway between Africa and Indonesia. Its central location in the Indian Ocean makes it a crucial military base, primarily for the United States and the United Kingdom, supporting operations across a vast maritime region.
The other oceans are geographically incorrect. The Atlantic Ocean lies between Europe/Africa and the Americas. The Pacific Ocean is the largest and is located between the Americas and Asia/Australia. The Arctic Ocean is situated around the North Pole. Diego Garcia's position is distinctly within the boundaries of the Indian Ocean, far from these other major bodies of water.