## Core Concept
The question targets the pharmacological management of uterine fibroids (myomas). Uterine fibroids are benign tumors that arise from the smooth muscle layer of the uterus, and their treatment can involve medical or surgical interventions. The focus here is on drugs that can reduce the size of myomas.

## Why the Correct Answer is Right
The correct answer, **Ulipristal acetate**, is a synthetic steroid that acts as a selective progesterone receptor modulator (SPRM). It has been shown to reduce the size of uterine fibroids by modulating the activity of progesterone, which plays a role in the growth of fibroids. Ulipristal acetate can induce fibroid shrinkage by promoting apoptosis (programmed cell death) in fibroid cells and reducing cell proliferation.

## Why Each Wrong Option is Incorrect
- **Option A:** While certain GnRH agonists can reduce the size of fibroids by inducing a hypoestrogenic state (since fibroids are estrogen-dependent), the specific mention of ulipristal acetate as the correct answer makes GnRH agonists less directly relevant here.
- **Option B:** This option might refer to another class of drugs, but without specifics, it's hard to directly refute. However, given the context, ulipristal acetate is specifically noted for its use in managing fibroids.
- **Option C:** This could potentially refer to other treatments, but similar to option B, without specifics, it's challenging to directly address. The focus remains on ulipristal acetate for size reduction.
- **Option D:** This option is a distractor and does not directly relate to the known treatments that reduce fibroid size like ulipristal acetate.

## Clinical Pearl / High-Yield Fact
A key point to remember is that ulipristal acetate is specifically used for the preoperative treatment of moderate to severe symptoms associated with uterine fibroids. It's also known for its use in emergency contraception. A notable clinical pearl is that ulipristal acetate can be used intermittently for up to 5 years for the treatment of symptomatic uterine fibroids, making it a valuable option for managing this condition.

## Correct Answer: C. Ulipristal acetate