Explanation:

- The given group of words: "Living or growing in water."

- Option 1: Submarine

- Definition: A watercraft designed for underwater operations.

- Not related to living organisms; it's a machine.

- Option 2: Mammal

- Definition: Warm-blooded vertebrates with hair/fur and typically give birth to live young.

- Not necessarily related to living in water; many are land animals.

- Option 3: Amphibian

- Definition: Cold-blooded vertebrates like frogs that live both in water and on land.

- Partially correct, but not exclusively living in water.

- Option 4: Aquatic

- Definition: Relates to living or growing in water.

- Specifically refers to life forms and plants that exist in water environments.