**Core Concept**
Fetal presentation refers to the part of the fetus that is closest to the birth canal during delivery. The attitude of the fetus is the position of its body in relation to the long axis of the fetus. Flexion is a common attitude in late pregnancy, where the fetus curls up with the knees bent and the head down.

**Why the Correct Answer is Right**
When the fetus is in a flexed attitude, the head is the presenting part. This is because the flexed position allows the head to pass through the birth canal more easily, reducing the risk of complications during delivery. In this position, the head is typically the first part of the fetus to enter the birth canal, followed by the body.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because extension, not flexion, would result in a different presenting part, such as the feet or buttocks.
**Option B:** This option is incorrect because a fetus in a flexed attitude would not present with the buttocks first.
**Option C:** This option is incorrect because a fetus in a flexed attitude would not present with the feet first.

**Clinical Pearl / High-Yield Fact**
In obstetrics, the attitude of the fetus is an important factor in determining the mode of delivery, as a flexed attitude may require a vaginal delivery, while an extended attitude may require a cesarean section.

**Correct Answer: C. Head.**