**Core Concept**
Breast milk composition is a crucial aspect of lactation, with varying amounts of carbohydrates, proteins, and fats. Lactose is a disaccharide sugar present in breast milk, serving as an essential energy source for infants.

**Why the Correct Answer is Right**
Lactose in breast milk is produced in the mammary glands through the action of the enzyme lactase, which breaks down glucose and galactose from the blood into lactose. The lactose content in breast milk is approximately 7 grams per 100 ml, making it an ideal source of energy for infants. This composition supports the growth and development of the infant's gut microbiome and provides a suitable energy source for their rapid growth.

**Why Each Wrong Option is Incorrect**
**Option A:** 0.7 grams per 100 ml - This is too low and does not accurately reflect the lactose content in breast milk.
**Option B:** 17 grams per 100 ml - This is excessively high and would lead to an excessive sugar load in the infant's diet.
**Option C:** 4 grams per 100 ml - This is lower than the actual lactose content in breast milk.

**Clinical Pearl / High-Yield Fact**
Breast milk composition changes over the first few days of lactation, with a decrease in lactose content as the infant's gut microbiome matures. This adaptation supports the infant's transition to a more complex diet.

**Correct Answer: D. 7 grams.**