**Core Concept**
Pulse proteins, also known as legume proteins, are derived from plants such as lentils, chickpeas, and beans. They are a vital source of protein in a vegetarian diet. However, pulse proteins are often deficient in certain essential amino acids.

**Why the Correct Answer is Right**
The correct answer is related to the fact that pulse proteins are typically low in one or more essential amino acids. This is because plants often lack certain amino acids that are present in animal-derived proteins. The most commonly deficient amino acid in pulse proteins is methionine, an essential amino acid that plays a critical role in various bodily functions.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately reflect the amino acid deficiency commonly associated with pulse proteins.
**Option B:** This option is also incorrect as it does not specify the correct amino acid deficiency.
**Option C:** Similarly, this option is incorrect as it does not accurately identify the deficient amino acid.

**Clinical Pearl / High-Yield Fact**
It is essential to note that a diet consisting only of pulse proteins can lead to protein malnutrition if the deficient amino acid is not supplemented through other dietary sources. Combining pulse proteins with other plant-based proteins, such as cereals, can help alleviate this issue.

**Correct Answer:** D. Methionine.