Question

select the words that best complete the sentences. sharks do not have a single bone in their bodies. instead, their skeleton is made entirely of cartilage. cartilage is the same material that the human nose and ears are composed of. cartilage weighs less than bone, allowing sharks to swim briskly while using less energy than if they had bones.

Explanation:

The context is about sharks' physical - characteristics and their swimming ability. Since cartilage is lighter than bone, it makes sense that sharks use less of a resource related to movement when swimming. "Energy" is the most appropriate word as it is related to the effort required for swimming.

Answer:

energy