Menstrual cycle occurs in

Options

A. old world monkeys
B. apes
C. humans
D. all of these

Answer

**Step-by-Step Solution:**

1. **Understanding the Menstrual Cycle**: The menstrual cycle refers to the series of changes that occur in the female reproductive system to prepare for potential pregnancy. This cycle involves hormonal changes, ovulation, and the shedding of the uterine lining if fertilization does not occur.

2. **Identifying the Organisms**: The question asks about the occurrence of the menstrual cycle in specific groups of organisms: old world monkeys, apes, and humans.

3. **Recognizing the Classification**: All the mentioned groups (old world monkeys, apes, and humans) belong to the primate order. Primates are known for having similar reproductive features, including the menstrual cycle.

4. **Confirming the Presence of the Menstrual Cycle**: Research and biological studies indicate that all primates exhibit a menstrual cycle. This includes:
- **Humans**: Female humans undergo a menstrual cycle as part of their reproductive process.
- **Apes**: Female apes also experience a menstrual cycle.
- **Old World Monkeys**: These monkeys also show a menstrual cycle.

5. **Conclusion**: Since all the groups mentioned in the options (old world monkeys, apes, and humans) exhibit the menstrual cycle, the correct answer to the question is "all of these."

**Final Answer**: The menstrual cycle occurs in all of these: old world monkeys, apes, and humans.

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