Concept:Gills are the respiratory organs that enable fish to extract dissolved oxygen from water.
Explanation:Fish need oxygen to survive.
Water contains dissolved oxygen.
Gills absorb this oxygen and remove carbon dioxide.
A streamlined body, scales, and paired fins help in movement and protection.
But they do not directly help in breathing underwater.
Without gills, fish cannot respire properly in water.
Therefore, gills are the main reason fish can survive in water.
Answer:D. gills