Which of the following molecules can be used by us as a source of energy?

Options

A. Carbohydrates only
B. Fats only
C. Carbohydrates or fats
D. Carbohydrates, fats and vitamins

Answer

To determine which molecules can be used by us as a source of energy, we need to analyze the types of nutrients and their roles in our body.

### Step-by-Step Solution:

1. **Understanding Nutrients**: Nutrients are classified into two main categories: macronutrients and micronutrients.
- **Macronutrients**: These include carbohydrates, proteins, and fats (lipids). They are required in larger amounts and provide energy.
- **Micronutrients**: These include vitamins and minerals. They are needed in smaller quantities and do not provide energy.

2. **Identifying Energy Sources**: Among the macronutrients:
- **Carbohydrates**: These are the primary source of energy for the body. They are broken down into glucose, which is used for energy.
- **Fats (Lipids)**: These are also a significant source of energy. They provide more energy per gram compared to carbohydrates.
- **Proteins**: While proteins can be used for energy, they are primarily used for growth and repair of tissues. In normal circumstances, they are not the first choice for energy.

3. **Evaluating the Options**: Based on the classification:
- If an option includes only carbohydrates, it is incomplete because fats also provide energy.
- If an option includes only fats, it is also incomplete for the same reason.
- An option that includes carbohydrates and fats is correct.
- An option that includes carbohydrates, fats, and vitamins is incorrect because vitamins do not provide energy.

4. **Conclusion**: The correct answer would be the option that includes both carbohydrates and fats, as these are the primary sources of energy for the body.

### Final Answer:
The molecules that can be used by us as a source of energy are **Carbohydrates and Fats**.

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