## Core Concept
In humans, carbohydrates are primarily stored in the form of **glycogen**, a complex carbohydrate that serves as the main storage form of glucose in the body. This storage occurs mainly in the liver and muscles. Glycogen is a polysaccharide composed of glucose units and is crucial for maintaining blood glucose levels and providing energy.

## Why the Correct Answer is Right
The correct answer, **glycogen**, is the primary storage form of carbohydrates in humans. It is synthesized from glucose through a process called glycogenesis and can be broken down back into glucose through glycogenolysis when energy is needed. This process is vital for energy metabolism and maintaining glucose homeostasis in the body.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is blank and does not provide a valid choice for carbohydrate storage form.
- **Option B:** This option is also blank and does not offer a correct or incorrect statement regarding carbohydrate storage.
- **Option C:** Similarly, this option is blank and lacks relevant information.

## Clinical Pearl / High-Yield Fact
A key point to remember is that **glycogen** is the main storage form of carbohydrates in humans, primarily found in the liver (about 100g) and muscles (about 400g). This storage form is critical for short-term energy needs and glucose homeostasis.

## Correct Answer Line
**Correct Answer: D. glycogen**