Select the option that can be used as a one-word substitute for the given group of words.

Animals that live in water

Aquatic

The term "aquatic" refers to animals or plants that live in water or are adapted to living in water environments. It specifically describes organisms that are associated with or found in water bodies such as oceans, rivers, lakes, and ponds. In the given group of words, "animals that live in water" indicates a specific habitat requirement, and the word "aquatic" perfectly captures that meaning.

"Nocturnal" describes organisms that are active during the night and rest or sleep during the day. It doesn't relate to the habitat in which the animals live.

"Aerial" refers to things related to the air or atmosphere. It describes organisms or objects that are associated with or found in the air, such as birds or aircraft. It doesn't represent animals living in water.

"Terrestrial" refers to organisms that live or are adapted to live on land. It describes animals that live on land, not in water.

Therefore, "Aquatic" is the most appropriate one-word substitute for the given group of words as it specifically indicates animals that live in water.