**Core Concept**
Mifepristone, also known as RU-486, is a synthetic steroid that acts as a potent antagonist of the progesterone receptor (PR). This pharmacological action makes it useful for various medical indications related to progesterone-dependent conditions.

**Why the Correct Answer is Right**
Mifepristone is primarily used for:
- Medical abortion: Mifepristone blocks the action of progesterone, necessary for maintaining pregnancy, thus facilitating abortion. It is often used in combination with misoprostol for this purpose.
- Cushing's syndrome: Exogenous administration of progesterone can exacerbate Cushing's syndrome, a condition caused by excessive cortisol levels. Mifepristone helps control cortisol levels in these patients.
- Cervical ripening: Mifepristone can induce cervical ripening by blocking progesterone's action, making it easier to induce labor.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not a valid indication for Mifepristone. Mifepristone is not used for treating hypothyroidism, a condition where the thyroid gland doesn't produce enough thyroid hormones.

**Option B:** This option is incorrect because Mifepristone is not used to treat polycystic ovary syndrome (PCOS). While PCOS is a condition related to hormonal imbalances, Mifepristone is not the preferred treatment for managing PCOS.

**Option C:** This option is incorrect because Mifepristone is not used to treat asthma. Mifepristone is not an anti-inflammatory agent, and its use in asthma would not be indicated.

**Clinical Pearl / High-Yield Fact**
Mifepristone has a unique mechanism of action as a progesterone receptor antagonist, which makes it useful for conditions where progesterone plays a crucial role. However, it's essential to remember that Mifepristone should not be used in pregnancy beyond the first trimester due to potential teratogenic effects.

**Correct Answer: A.**