What are the 3 types of variables ?

The fish shown above is a tarpon. it is a fast-swimming and powerful open-water fish. its closest relatives, oddly, are burrow-dwelling conger eels that stay on the bottom. both eels and tarpon developed from snake-like larvae that float in the plankton during the first stages of life. once they mature, tarpon and eels are not found near one another in the ocean. the tarpon and the eel illustrate all of the following except

What is the most appropriate method of gaining weight (muscle mass)

Is there any species that went extinct in recent years due to natural causes (not caused by human interaction). if so, what caused it?