Explanation:

Mammals are the class of vertebrate animals characterized by the presence of sweat glands, including sweat glands modified for milk production, hair, three middle ear bones used in hearing, and aneocortex region in the brain.

Sea Cow:- Sea Cow (Hydrodamalis gigas), also called Steller’s sea cow, very large aquatic mammal.

Sea Horse:- Sea horse is a vertabrate fish .

Sea Lion:- It is warm blooded, gives birth to live young, has hair, and the female produces milk.

So option 2 is correct.