Questions: Triglycerides

The answer is the fourth one: Triglycerides.

Explanation for each option:

1. Sterols: These are a subgroup of steroids and an important class of organic molecules. They are not primarily used for energy storage but play a role in cell membrane structure and function, as well as in the synthesis of hormones.
2. Fatty acids: These are the building blocks of fats and are used for energy, but they are not the main storage form of energy in the body. They are components of triglycerides.
3. Phospholipids: These are a major component of cell membranes and are not used primarily for energy storage. They play a crucial role in cell structure and function.
4. Triglycerides: These are the main storage form of energy in the body. They are stored in adipose tissue and can be broken down into fatty acids and glycerol to provide energy when needed.

Summary: Triglycerides are the body's main storage form of energy, making them the correct answer.