**Core Concept**
The second stage of labor refers to the period from full cervical dilation (10 cm) to the delivery of the fetus. This stage involves intense uterine contractions that facilitate fetal expulsion.

**Why the Correct Answer is Right**
During the second stage of labor, the cervix is fully dilated, and the fetal head is visible at the introitus. The uterus contracts vigorously, helping to push the baby out. The cervix becomes effaced and thinned, allowing the baby's head to pass through. The mother may feel overwhelming pressure to push, and with each contraction, the baby descends further into the birth canal.

**Why Each Wrong Option is Incorrect**
**Option A:** This is incorrect as the first stage of labor involves cervical dilation from 0 to 10 cm, which is not the focus of the second stage.
**Option B:** This is incorrect as the third stage of labor refers to the period after delivery of the fetus and before delivery of the placenta, which is not relevant to the second stage.

**Clinical Pearl / High-Yield Fact**
It's essential to recognize the distinct characteristics of each stage of labor to provide effective support and care to the mother. The second stage of labor typically lasts around 1-2 hours, but this can vary significantly between women.

**Correct Answer: A.**