**Core Concept**
A classical cesarean section involves a vertical incision in the upper segment of the uterus, which is typically reserved for specific indications where a lower segment transverse incision is not feasible. This type of incision is often associated with increased risk of uterine rupture in future pregnancies.

**Why the Correct Answer is Right**
Dense adhesions in the lower uterine segment can lead to a failed lower segment transverse incision, necessitating a classical cesarean section. This is because the presence of adhesions can compromise the integrity of the lower uterine segment, making it difficult to safely perform a transverse incision. In such cases, a classical incision is preferred to ensure a safe delivery. The lower uterine segment is more prone to adhesions, especially in cases of previous uterine surgery, such as a previous cesarean section.

**Why Each Wrong Option is Incorrect**
**Option A:** Transverse lie is a condition where the fetus is positioned with its feet or buttocks facing the mother's spine, which is not a direct indication for a classical cesarean section. In most cases, a transverse lie can be managed with external cephalic version (ECV) or a lower segment transverse cesarean section.

**Option B:** Cord prolapse is a medical emergency that requires immediate delivery, but it is not an indication for a classical cesarean section. In fact, a classical incision may not be the best option in this scenario due to the urgency of the situation.

**Option D:** Placenta praevia is a condition where the placenta covers the cervix, which may require a cesarean section. However, it is not an indication for a classical incision, and a lower segment transverse incision is often sufficient.

**Clinical Pearl / High-Yield Fact**
In cases of previous uterine surgery, such as a previous cesarean section, dense adhesions in the lower uterine segment are a common indication for a classical cesarean section. This is because the presence of adhesions can compromise the integrity of the lower uterine segment, making it difficult to safely perform a transverse incision.

✓ Correct Answer: C. Dense adhesions in lower uterine segment