**Core Concept**
The core concept being tested here is the evaluation of protein quality, which is a critical aspect of nutrition and biochemistry. Protein quality is determined by its ability to support growth, maintenance, and repair of body tissues, and is often assessed by measuring the protein's digestibility and its ability to provide essential amino acids.

**Why the Correct Answer is Right**
The best method to compare protein quality is the net protein utilization (NPU) method. NPU is calculated by measuring the ratio of nitrogen retained to the nitrogen ingested, and it takes into account both the digestibility and the biological value of the protein. This method provides a comprehensive assessment of protein quality and is widely used in nutritional research and clinical settings.

**Why Each Wrong Option is Incorrect**
**Option A:**
This option is incorrect because the biological value (BV) method only measures the proportion of absorbed nitrogen that is retained by the body and does not take into account the digestibility of the protein. Therefore, it is not a comprehensive measure of protein quality.

**Option B:**
This option is incorrect because the protein efficiency ratio (PER) method measures the weight gain of an animal on a specific protein diet over a period of time, but it does not account for the protein's digestibility or its ability to provide essential amino acids.

**Option C:**
This option is incorrect because the protein digestibility corrected amino acid score (PDCAAS) method is a more recent and refined method of evaluating protein quality, but it is not the best method for comparing protein quality among different sources.

**Clinical Pearl / High-Yield Fact**
The NPU method is a comprehensive measure of protein quality that takes into account both the digestibility and the biological value of the protein. This method is widely used in nutritional research and clinical settings to evaluate the quality of dietary proteins.

**Correct Answer: C. NPU (Net Protein Utilization)**