**Core Concept**
The F-75 milk formula is a type of nutritional supplement used in emergency situations to provide essential nutrients to malnourished children. The protein content in F-75 milk formula is a critical component that helps in the recovery of children from malnutrition.

**Why the Correct Answer is Right**
The F-75 milk formula contains 10-12 grams of protein per liter, which is essential for the growth and development of children. The protein content in F-75 is derived from a combination of skimmed milk powder and vegetable oils. The protein is broken down into essential amino acids, which are then absorbed by the body to promote growth and repair of tissues.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as the protein content in F-75 is not 5-6 grams per liter, which is insufficient for the nutritional needs of children.
**Option B:** This option is incorrect as the protein content in F-75 is not 15-16 grams per liter, which is excessive and may cause gastrointestinal side effects.
**Option C:** This option is incorrect as the protein content in F-75 is not 20-22 grams per liter, which is not recommended for children in emergency situations.

**Clinical Pearl / High-Yield Fact**
It is essential to note that the protein content in F-75 milk formula should not exceed 12 grams per liter to avoid gastrointestinal side effects and ensure optimal absorption of nutrients.

**Correct Answer: D. 12 grams per liter.**