**Core Concept**
The question requires knowledge of the protein content in different types of food. Protein is a crucial macronutrient essential for various bodily functions, including growth, repair, and maintenance of tissues. The protein content in food can vary significantly depending on the source and type.

**Why the Correct Answer is Right**
The correct answer is **C. Egg**. Eggs are considered one of the richest sources of protein, with approximately 6-7 grams of protein per large egg. This high protein content makes eggs an excellent choice for individuals looking to increase their protein intake. The protein in eggs is primarily composed of albumin and globulin, which are both essential for various bodily functions.

**Why Each Wrong Option is Incorrect**
**Option A:** While meat is a good source of protein, it generally contains less protein than eggs per 100 grams. For example, chicken breast contains about 3-4 grams of protein per 100 grams.

**Option B:** Nuts and seeds are a good source of protein, but they generally contain less protein than eggs per 100 grams. For example, almonds contain about 2-3 grams of protein per 100 grams.

**Option D:** Legumes are a good source of protein, but they generally contain less protein than eggs per 100 grams. For example, lentils contain about 2-3 grams of protein per 100 grams.

**Clinical Pearl / High-Yield Fact**
It's essential to note that the protein content in food can vary depending on the cooking method and preparation. For example, boiling eggs can reduce the protein content, while frying can increase it.

**Correct Answer:** . Egg