**Core Concept**
The expected date of delivery (EDD) is a crucial concept in obstetrics, calculated to estimate the time of birth based on the gestational age at the last menstrual period (LMP) or ultrasound dating. It's essential to understand the principles of fetal development and the timeline of pregnancy to accurately predict EDD.

**Why the Correct Answer is Right**
The correct answer is based on the fact that the EDD is calculated by adding 7 days to the first day of the LMP, assuming a 28-day menstrual cycle, and then subtracting 3 months (approximately 3 weeks) to account for the 2 weeks of amenorrhea before ovulation. This method is based on the fact that conception typically occurs 2 weeks after the start of the LMP.

**Why Each Wrong Option is Incorrect**
* **Option A:** This statement is true and forms the basis of the EDD calculation.
* **Option B:** This statement is also true as it's a common method used to estimate gestational age.
* **Option D:** This statement is true as well, as ultrasound dating is an essential tool in obstetrics to confirm gestational age.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that the EDD is an estimate, and the actual date of delivery can vary by up to 2 weeks from the calculated date. This is why it's essential to confirm gestational age through ultrasound dating, especially in cases where the LMP is uncertain.

**Correct Answer: C.**