**Core Concept**
The extra energy requirement during lactation is crucial for both the mother's health and the production of milk for the infant. Lactation is an energy-intensive process, requiring additional calories beyond the mother's normal basal metabolic rate. The World Health Organization provides guidelines on the increased energy needs during this period.

**Why the Correct Answer is Right**
The correct answer is based on the recommended dietary allowance that accounts for the increased energy expenditure associated with milk production. Generally, an additional 500-600 Kcal/d is recommended for the first six months of lactation, but this can vary based on factors such as the mother's pre-pregnancy weight, activity level, and the infant's age and weight.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it underestimates the energy requirements.
**Option B:** This option overestimates the energy needs for the first three months of lactation.
**Option D:** This option significantly overestimates the required energy increase.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that the energy requirements during lactation can vary, but generally, an increase of about 500 Kcal/d is recommended for well-nourished mothers. This is crucial for supporting both maternal health and adequate milk production for the infant.

**Correct Answer:** B. 500 Kcal/d