Which one of the following pairs belongs to cartilaginous fish?

Answer: Option B

The correct answer is Option B: Shark and ray.
Here's why:
Cartilaginous fish are a group of fish that have skeletons made of cartilage instead of bone.
Cartilage is a flexible tissue.
Sharks and rays are both well-known examples of cartilaginous fish.
Tuna, hilsa, and eel are bony fish, meaning their skeletons are made of bone.
Skates are related to rays and are also cartilaginous fish.
However, option C includes hilsa, which is a bony fish, making it incorrect.
Therefore, the only pair that includes exclusively cartilaginous fish is Shark and ray.