Oral contraceptives prevent pregnancy by:

Options

A. Killing the ovum
B. Blocking fertilization
C. Preventing ovulation
D. Preventing implantation

Answer

**Step-by-Step Solution:**

1. **Understanding Oral Contraceptives**: Oral contraceptives are medications taken by women to prevent pregnancy. They often contain hormones that regulate the reproductive system.

2. **Example of Oral Contraceptive**: One well-known example of an oral contraceptive is "Saheli," which is considered safe and has minimal side effects.

3. **Mechanism of Action**: The primary way oral contraceptives prevent pregnancy is through the use of synthetic hormones, particularly progesterone.

4. **Role of Progesterone**: Progesterone works by preventing ovulation. Ovulation is the process where an ovary releases an egg. If ovulation does not occur, there is no egg available for fertilization, thus preventing pregnancy.

5. **Elimination of Other Options**:
- **Killing the Ovum**: Oral contraceptives do not kill the ovum; they prevent its release.
- **Termination of Unwanted Pregnancy**: This is not applicable as oral contraceptives do not terminate an existing pregnancy.
- **Blocking Fertilization**: This is not the primary action of oral contraceptives; they do not block fertilization directly.
- **Preventing Implantation**: Oral contraceptives do not prevent implantation of a fertilized egg; their main function is to prevent ovulation.

6. **Conclusion**: Therefore, the correct answer to the question "Oral contraceptives prevent pregnancy by:" is "Preventing Ovulation."

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