……... is the building block of carbohydrates.

Options

A. Monosaccharide
B. Amino acid
C. Glycerol
D. Fatty acid

Explanation

**Step-by-Step Solution:**

1. **Understanding Carbohydrates**: Carbohydrates are organic compounds that consist of carbon, hydrogen, and oxygen. They are essential macromolecules that provide energy to living organisms.

2. **Identifying the Building Blocks**: The fundamental units that make up carbohydrates are known as monosaccharides. These are the simplest form of carbohydrates and cannot be hydrolyzed into simpler sugars.

3. **Types of Carbohydrates**:
- **Monosaccharides**: Single sugar molecules (e.g., glucose, fructose).
- **Disaccharides**: Formed when two monosaccharides bond together (e.g., sucrose).
- **Polysaccharides**: Large molecules made up of many monosaccharides linked together (e.g., starch, glycogen).

4. **Conclusion**: Since monosaccharides are the simplest form of carbohydrates and serve as their building blocks, the answer to the question is "monosaccharides".

**Final Answer**: Monosaccharides are the building blocks of carbohydrates.

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