**Core Concept:** Human milk and cow's milk are different in terms of composition due to variations in the nutritional requirements of the infant. Human milk is more suitable for human babies, while cow's milk is designed for calves. Human milk contains a higher concentration of essential nutrients and immunoglobulins required for the development of an immature human infant.

**Why the Correct Answer is Right:** Human milk is more suitable for human infants because it is closer in composition to the human digestive system and immune system. It contains a higher concentration of lactase, enzymes that break down lactose, reducing lactose intolerance in infants. Additionally, human milk contains higher levels of immunoglobulins, which help protect infants from infections and diseases. These immunoglobulins are not present in significant amounts in cow's milk.

**Why Each Wrong Option is Incorrect:**
A. Incorrect, as human milk is more suitable for infants due to its closer similarity to human physiology and higher concentration of essential nutrients.
B. Incorrect, as cow's milk is designed for calves and lacks the nutrients and immunoglobulins required for human infants' development.
C. Incorrect, as human milk has a higher concentration of lactase and immunoglobulins, making it more suitable for infants.
D. Incorrect, as human milk is more suitable for human infants due to its closer composition to human physiology and higher nutrient content.

**Clinical Pearl:** The correct nutritional source for infants is human milk, as it closely matches the human digestive and immune systems, providing essential nutrients and immunoglobulins that are crucial for the physiological development of infants. Any attempt to feed infants with cow's milk should be done with caution, as it may lead to malnutrition and immune system deficiencies.