**Core Concept**
Postcoital contraceptives are emergency contraceptive methods used to prevent pregnancy after unprotected sex. They work by inhibiting or delaying ovulation, altering the endometrium, or interfering with fertilization or implantation.

**Why the Correct Answer is Right**
Emergency contraceptive pills (ECPs) containing levonorgestrel (Plan B) are the most common form of postcoital contraception. These pills work by primarily inhibiting or delaying ovulation through the inhibition of the luteinizing hormone (LH) surge. This action prevents the release of an egg from the ovary, thus preventing fertilization.

**Why Each Wrong Option is Incorrect**
**Option A:** This option might be a distractor, but it's not explicitly mentioned. If we consider an option like "IUD" (intrauterine device), it's incorrect because IUDs are not typically categorized as postcoital contraceptives. They are used for long-term contraception and can be inserted before or after the onset of menstruation.

**Option B:** This option is likely a distractor, but if we consider an option like "Hormonal IUDs", it's incorrect because they are not typically categorized as postcoital contraceptives. They are used for long-term contraception, and their primary mechanism is to thicken cervical mucus and prevent sperm penetration.

**Option C:** This option is likely a distractor, but if we consider an option like "Copper IUDs", it's incorrect because they are not typically categorized as postcoital contraceptives. They are used for long-term contraception and can be inserted before or after the onset of menstruation.

**Clinical Pearl / High-Yield Fact**
The most effective postcoital contraceptive method is the ECPs containing levonorgestrel (Plan B) when taken within 72 hours of unprotected sex. However, the copper IUD (ParaGard) is also effective when inserted within 5 days of unprotected sex.

**Correct Answer:** D.