In which of the following animal the endoskeleton is made of cartilage only?

Sharks belong to the class Chondriochthyes, which is a group of fishes that have a cartilaginous endoskeleton. Sharks, rays, skates, and chimera are all classified as Chondriochthyes. 

The whale is an aquatic mammal having an endoskeleton of bones while the snail is an invertebrate belonging to phylum Mollusca and lacks an endoskeleton of bones or cartilage. 

Gorilla is a mammal and has an endoskeleton of bones and cartilage.