**Core Concept**
RU-486, also known as mifepristone, is a potent antiprogesterone compound that blocks the progesterone receptor, leading to the termination of pregnancy. This action is crucial for inducing abortion.

**Why the Correct Answer is Right**
Mifepristone works by competitively binding to the progesterone receptor in the uterus, thereby preventing the necessary progesterone-mediated effects that maintain pregnancy. This results in the thinning of the uterine lining, making it less hospitable for implantation and growth of the embryo. In combination with a prostaglandin analog, such as misoprostol, mifepristone is effective in inducing abortion up to 49 days of gestation. This combination effectively terminates pregnancy by causing uterine contractions and cervical dilation.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the efficacy of mifepristone in inducing abortion decreases significantly beyond 49 days of gestation.
**Option B:** This option is incorrect because while mifepristone can be used in conjunction with a prostaglandin analog, it is not effective as a standalone medication for inducing abortion.
**Option D:** This option is incorrect because the efficacy of mifepristone in inducing abortion is not limited to early pregnancy; it is effective up to 49 days of gestation.

**Clinical Pearl / High-Yield Fact**
Mifepristone is often used in combination with a prostaglandin analog, such as misoprostol, to induce abortion up to 49 days of gestation. This combination is effective in terminating pregnancy by causing uterine contractions and cervical dilation.

**Correct Answer: C. 49 days**