## Core Concept
The assessment of protein quality and quantity can be evaluated through various methods. These methods help in understanding the nutritional value of proteins, especially in the context of dietary requirements and health.

## Why the Correct Answer is Right
The correct answer involves understanding what each option represents in terms of protein assessment:
- **Protein energy ratio** refers to the proportion of energy in the diet that comes from protein. It's an important factor in nutritional science but not a direct measure of protein quality.
- **BUN (Blood Urea Nitrogen)** is a waste product that occurs when the body breaks down protein. High levels can indicate kidney problems but also reflect protein intake.
- **Per gm calories given** relates to the energy density of protein, which is approximately 4 kcal/g. This is more about the quantity of energy provided by protein rather than its quality.
- **Amino acid score**, also known as the amino acid profile or chemical score, is a direct measure of the quality of a protein source. It compares the amino acid composition of a protein to a reference amino acid profile, usually the FAO/WHO reference profile.

## Why Each Wrong Option is Incorrect
- **Option A:** While the protein energy ratio (a) and per gm calories given (c) provide information on the dietary contribution and energy yield of proteins, they do not directly assess protein quality.
- **Option B:** BUN (b) is more of an indicator of kidney function and nitrogen balance rather than a direct measure of protein quality.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the **amino acid score (d)** is a critical measure of protein quality. It helps in identifying proteins that are limiting in certain essential amino acids, which is crucial for growth, repair, and maintenance of body tissues.

## Correct Answer: D. Amino acid score