At the time of fertilization.

Options

A. First maturation division is completed
B. Embryo is formed
C. Second maturation division is completed
D. First polar body is formed.

Answer

**Step-by-Step Solution:**

1. **Understanding Fertilization**: Fertilization is the process where a sperm cell (male gamete) penetrates an egg cell (female gamete), leading to the formation of a zygote. This is the initial step in the development of an embryo.

2. **Identifying the Maturation Divisions**:
- The **first maturation division** occurs during oogenesis (the formation of the egg) and results in the formation of the first polar body and a secondary oocyte.
- The **second maturation division** occurs only after fertilization, when the secondary oocyte completes its division to form the ovum and the second polar body.

3. **Evaluating the Options**:
- **Option A**: "First maturation division is complete" - This occurs before fertilization, so it is incorrect.
- **Option B**: "Embryo is formed" - An embryo is formed after fertilization, not at the time of fertilization, so this is incorrect.
- **Option C**: "Second maturation division is completed" - This is correct because the second maturation division of the ovum is completed at the time of fertilization.
- **Option D**: "First polar body is formed" - This happens during the first maturation division, which occurs prior to fertilization, making it incorrect.

4. **Conclusion**: The correct answer is **Option C: second maturation division is completed**.

---