Answer:

Sharks skeleton is made of cartilage instead of bones to have a lighter weight which allows them to go up and down quickly in the ocean without a lot of effort to stay afloat.

Cartilage is robust but not as dense as bone which gives them a great flexibility that allows them bending much easier than bony fishes. Such elasticity also gives them more speed as tails can move faster to propel them through the water.

 

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