**Core Concept**
Emergency contraception refers to the use of medications or devices to prevent pregnancy after unprotected sex or a known or suspected contraceptive failure. The goal is to delay or prevent ovulation, fertilization, or implantation of a fertilized egg.

**Why the Correct Answer is Right**
The emergency contraceptive of choice is **Levonorgestrel (Plan B)**, a progestin-only pill. It works by delaying or inhibiting ovulation, thereby preventing fertilization. Levonorgestrel acts by:
* Inhibiting the surge of luteinizing hormone (LH), which triggers ovulation
* Thickening cervical mucus, making it difficult for sperm to reach the egg
* Possibly affecting fertilization and implantation

**Why Each Wrong Option is Incorrect**
**Option A:** Not specified. This option is incomplete and cannot be evaluated.

**Option B:** Ethinyl estradiol. While ethinyl estradiol is a component of combined oral contraceptives, it is not the preferred emergency contraceptive due to its potential to induce vomiting and its lower efficacy compared to progestin-only pills like levonorgestrel.

**Option C:** Copper IUD (intrauterine device). While the copper IUD is an effective emergency contraceptive, it is typically inserted within 5-7 days after unprotected sex and requires a medical professional to insert it. Levonorgestrel is a more accessible and immediate option.

**Option D:** Not specified. This option is incomplete and cannot be evaluated.

**Clinical Pearl / High-Yield Fact**
Emergency contraception is most effective when used within 72 hours (3 days) after unprotected sex. The sooner it is used, the better the chances of preventing pregnancy.

**Correct Answer: C. Copper IUD (intrauterine device)**