**Core Concept**
The application of forceps in obstetrics requires careful consideration of various factors to ensure a safe and successful delivery. One key prerequisite is the proper alignment of the fetal head within the pelvis, which is essential for effective forceps delivery.

**Why the Correct Answer is Right**
The correct answer, **Option C**, is incorrect because the sagittal suture should not be in line with the transverse diameter of the pelvis. In fact, the sagittal suture should be in line with the anteroposterior diameter of the pelvis, not the transverse diameter. This is because the anteroposterior diameter is the largest diameter of the pelvis, making it the most suitable for the passage of the fetal head. When the sagittal suture is aligned with the transverse diameter, it increases the risk of complications, such as cephalopelvic disproportion and fetal distress.

**Why Each Wrong Option is Incorrect**
**Option A:** The aftercoming head of a breech is, in fact, a prerequisite for applying forceps in a breech delivery. It is essential to ensure that the aftercoming head is in the correct position before attempting to apply forceps.

**Option B:** There should indeed be no cephalopelvic disproportion (CPD) before applying forceps. CPD refers to a condition where the fetal head is too large to pass through the mother's pelvis, making forceps delivery contraindicated.

**Option D:** The fetal head should be engaged before applying forceps. Engagement refers to the process by which the fetal head moves down into the pelvis, aligning with the mother's pelvis.

**Clinical Pearl / High-Yield Fact**
When applying forceps, it is essential to ensure that the sagittal suture is in line with the anteroposterior diameter of the pelvis, not the transverse diameter. This is a critical distinction that can make or break a successful forceps delivery.

**Correct Answer Line**
✓ Correct Answer: C. Saggital suture should be in line with transverse diameter of pelvis