Animals store most of their excess energy reserves as because

a) glucose; it is easy to break down.
b) fat; they store twice as much energy per gram.
c) protein; it is a compact source of energy in their bodies.
d) carbohydrates; they store twice as much energy per gram of glucose.

The answer to this question would be: B)fat; they store twice as much energy per gram. 

Fat can be converted into much more calorie than glucose or protein. Glucose and protein rate would be 4kcal/grams but fat can give 9kcal/grams which were about 2 times more.
But carbohydrate would be the primary source of energy in the human diet. If the energy is more than the body needs, it will be converted into fat.