**Core Concept**
The increased calorie requirements during pregnancy are due to the additional energy needs of the fetus, placenta, and maternal tissues. This increase in energy demand supports the growth and development of the fetus, as well as the changes in maternal metabolism.

**Why the Correct Answer is Right**
The correct answer is based on the recommended dietary allowance (RDA) for pregnant women, which suggests an increase of approximately 300 kcal/day above the non-pregnant requirement. This increased energy intake is necessary to support fetal growth, maternal tissue deposition, and the increased metabolic rate associated with pregnancy.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not provide sufficient additional calories to support fetal growth and development.
**Option B:** This option is also incorrect as it exceeds the recommended increase in calorie requirements.
**Option D:** Similarly, this option is incorrect as it does not align with the RDA for pregnant women.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that the increased calorie requirements during pregnancy are crucial for preventing maternal and fetal complications, such as low birth weight and maternal malnutrition.

**Correct Answer:** C. 300 kcal/day