**Core Concept**
Emergency contraception primarily aims to prevent pregnancy after unprotected sex or contraceptive failure. It works by altering the physiological processes that lead to fertilization and implantation of a fertilized egg. The mechanisms of emergency contraception can be multifaceted, involving various physiological and biochemical pathways.

**Why the Correct Answer is Right**
Option A, "By Causing early ovulation," is incorrect because emergency contraception does not induce premature ovulation. Instead, most emergency contraceptives, such as levonorgestrel, work by inhibiting or delaying ovulation, thereby preventing the release of an egg that could be fertilized. The primary mechanism of action of emergency contraception involves the inhibition of ovulation, fertilization, or implantation of a fertilized egg.

**Why Each Wrong Option is Incorrect**
**Option B:** Degeneration of corpus luteum is a secondary effect of emergency contraception, not its primary mechanism. The corpus luteum produces progesterone, which is essential for preparing the uterus for implantation of a fertilized egg. Degeneration of the corpus luteum is an indirect consequence of emergency contraception, not a direct mechanism.

**Option C:** Inhibition of fertilization is a correct mechanism of emergency contraception. Many emergency contraceptives, including levonorgestrel and ulipristal acetate, work by interfering with the fertilization process, thereby preventing the formation of a zygote.

**Option D:** Prevention of implantation of a fertilized egg is another correct mechanism of emergency contraception. Some emergency contraceptives, such as mifepristone, work by blocking the action of progesterone, which is essential for implantation of a fertilized egg.

**Clinical Pearl / High-Yield Fact**
It is essential to note that emergency contraception is not a substitute for regular contraception. Women should use reliable methods of contraception to prevent unintended pregnancy. Emergency contraception should be used only in cases of unprotected sex or contraceptive failure.

**✓ Correct Answer: A. By Causing early ovulation. This option is incorrect as emergency contraception does not induce premature ovulation.**