## Core Concept
The net protein utilization (NPU) is a measure of the ratio of amino acids converted to proteins to the ratio of amino acids supplied. It essentially reflects how efficiently the body can use the protein from a particular food source. Different foods have different NPU values based on their amino acid profiles.

## Why the Correct Answer is Right
Rice is known for being low in lysine, an essential amino acid. This limitation affects its NPU value. The NPU of rice is generally reported to be around 0.55 to 0.60, or 55% to 60%. This means that out of the total protein content in rice, approximately 55% to 60% is utilized by the body for protein synthesis. The correct answer reflects this utilization efficiency.

## Why Each Wrong Option is Incorrect
- **Option A:** This option suggests a much higher NPU than what is known for rice. An NPU of 90% or higher is characteristic of high-quality proteins like those found in eggs or milk, not rice.
- **Option B:** This option might seem plausible but still overestimates the NPU of rice. While it's closer, it doesn't accurately reflect the known limitations in the amino acid profile of rice.
- **Option D:** This option underestimates the NPU of rice. While rice does have a lower NPU compared to complete protein sources, its value is higher than what this option suggests.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the limiting amino acid in rice is **lysine**. This is crucial for understanding not just the NPU of rice but also how to complement its protein with other foods to achieve a balanced amino acid intake. For example, combining rice with legumes (which are often low in methionine but high in lysine) can result in a more balanced protein intake.

## Correct Answer: B. 57%