**Core Concept**
The question is testing the underlying cause of menorrhagia in puberty, which is a common gynecological issue. Menorrhagia refers to abnormally heavy menstrual bleeding, and identifying its causes is crucial for effective management.

**Why the Correct Answer is Right**
The correct answer is **C. Anovulatory cycles**. During puberty, the hypothalamic-pituitary-ovarian axis is still developing, leading to irregular menstrual cycles. Anovulatory cycles, where the ovaries do not release an egg, result in unopposed estrogen production, causing endometrial hyperplasia and subsequent heavy menstrual bleeding. This is a common cause of menorrhagia in adolescents.

**Why Each Wrong Option is Incorrect**
* **Option A:** Polycystic Ovary Syndrome (PCOS) is a common cause of menstrual irregularities, but it is not the most common cause of menorrhagia in puberty.
* **Option B:** Uterine anomalies, such as a septate uterus, can cause heavy menstrual bleeding, but they are relatively rare in adolescents.
* **Option D:** Coagulation disorders, such as von Willebrand disease, can cause excessive bleeding, but they are not a common cause of menorrhagia in puberty.

**Clinical Pearl / High-Yield Fact**
It is essential to note that menorrhagia in adolescents can be a sign of underlying hormonal imbalances or anatomical abnormalities, and a thorough evaluation, including a pelvic exam, ultrasound, and hormonal assays, is necessary to determine the underlying cause.

**Correct Answer: C. Anovulatory cycles**