## Core Concept
Mifepristone, also known as RU-486, is a **synthetic steroid** and a **progestin receptor antagonist**. It is primarily used for **medical abortion** and in the management of **Cushing's syndrome**. Its mechanism of action involves blocking the **progesterone receptor**, which is essential for maintaining pregnancy.

## Why the Correct Answer is Right
Mifepristone works by competitively inhibiting the binding of **progesterone** to its receptor, which is crucial for the maintenance of pregnancy. This leads to the **sloughing of the endometrium** and ultimately results in the termination of pregnancy. In the context of Cushing's syndrome, mifepristone helps by blocking the effects of **excess cortisol**.

## Why Each Wrong Option is Incorrect
- **Option A:** Without the specific details of option A, it's challenging to provide a direct explanation. However, any option that does not accurately describe a recognized use or mechanism of mifepristone would be incorrect based on the established pharmacological profile of the drug.
- **Option B:** Similarly, without specifics, if option B inaccurately represents a characteristic of mifepristone, such as its receptor activity or clinical application, it would be considered incorrect.
- **Option D:** This option would be incorrect if it suggests a use or mechanism not supported by clinical evidence or pharmacological understanding of mifepristone.

## Clinical Pearl / High-Yield Fact
A key point to remember is that mifepristone is effective for **medical abortion** within a specific gestational age limit (typically up to 49 days of gestation) and for the treatment of **endogenous Cushing's syndrome** in adults with **diabetes mellitus type 2** or glucose intolerance. Its use requires careful patient selection and follow-up.

## Correct Answer Line
**Correct Answer: C.**