**Core Concept**
Human milk is a complex mixture of nutrients, immunoglobulins, and hormones that provide optimal nutrition for the growth and development of infants. The caloric content of human milk is essential for meeting the energy needs of the infant.

**Why the Correct Answer is Right**
Human milk contains approximately 70 kcal/100 ml, which is ideal for infant growth and development. This caloric content is achieved through a balance of carbohydrates (lactose), fats (triglycerides), and proteins (casein and whey). The caloric content of human milk is adjusted according to the infant's age and needs, with higher caloric content in milk from mothers of preterm infants.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as human milk contains significantly more calories than 20 kcal/100 ml.
**Option B:** This option is incorrect as human milk contains approximately 70 kcal/100 ml, not 50 kcal/100 ml.
**Option C:** This option is incorrect as human milk contains a balanced mixture of carbohydrates, fats, and proteins, not just 90 kcal/100 ml of carbohydrates.

**Clinical Pearl / High-Yield Fact**
Human milk is often referred to as "liquid gold" due to its optimal nutrient profile and immunological benefits for infants. The caloric content of human milk can vary depending on maternal diet, lactation stage, and infant age.

**Correct Answer: B. 70 kcal/100 ml**