Animals store energy by making a polymer called glycogen. which best describes the structure of glycogen?

Glycogen is a  polymer of glucose and it has branched structure.

Explanation:

Glycogen is made up of repetitive units of glucose. IT is a polysaccharide.

The glucose molecules are bonded by glycosidic bonds.

There is a linear chain of Glucose molecules residues are linked linearly by α-1,4 glycosidic linkages. the branching starts after 10-12 glucose units by  α-1,6 glycosidic linkages.