All carbohydrates are composed of one or more:

• A. Monosaccharide units
• B. Amino acids
• C. Nucleotides
• D. Fatty acids

Answer: (A)

Verified step by step guidance

1. Understand the definition of carbohydrates: Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen, typically in a ratio of 1:2:1. They serve as a primary energy source and structural components in living organisms.
2. Learn the building blocks of carbohydrates: Carbohydrates are composed of monosaccharide units, which are simple sugars such as glucose, fructose, and galactose. These monosaccharides can combine to form disaccharides (e.g., sucrose) or polysaccharides (e.g., starch, cellulose).
3. Differentiate carbohydrates from other biomolecules: Amino acids are the building blocks of proteins, nucleotides are the building blocks of nucleic acids (DNA and RNA), and fatty acids are components of lipids. These are distinct from carbohydrates and serve different biological functions.
4. Recognize the correct answer: Since carbohydrates are composed of monosaccharide units, the correct answer is 'Monosaccharide units.' The other options (amino acids, nucleotides, and fatty acids) are not relevant to carbohydrate structure.
5. Apply this knowledge to future questions: When identifying the composition of biomolecules, focus on their specific building blocks (e.g., monosaccharides for carbohydrates, amino acids for proteins, etc.) to avoid confusion.