Assertion (A): Oxytocin helps in parturition.
Reason (R): Oxytocin acts on uterine muscle and causes expulsion of the foetus.

Options

A. Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion(A).
B. Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
C. Assertion (A) is true but reason (R) is false.
D. Assertion (A) is false but reason (R) is true.

Explanation

To solve the question regarding the assertion and reason related to oxytocin and parturition, we can break down the solution into the following steps:

### Step-by-Step Solution:

1. **Identify the Assertion and Reason**:
- Assertion (A): Oxytocin helps in parturition.
- Reason (R): Oxytocin acts on uterine muscle and causes expulsion of the fetus.

2. **Understand the Role of Oxytocin**:
- Oxytocin is a hormone produced in the hypothalamus and stored in the posterior pituitary gland. It plays a crucial role during childbirth (parturition).

3. **Explain the Mechanism of Action**:
- During labor, the contractions of the uterine muscles begin. Oxytocin is released in response to these contractions, which leads to a positive feedback mechanism.
- The release of oxytocin increases the strength and frequency of uterine contractions, which is essential for the process of childbirth.

4. **Link the Reason to the Assertion**:
- The reason provided states that oxytocin acts on the uterine muscles and causes the expulsion of the fetus. This directly supports the assertion that oxytocin helps in parturition.
- Therefore, both the assertion and the reason are true, and the reason serves as an explanation for the assertion.

5. **Conclusion**:
- Since both the assertion and the reason are true, and the reason explains the assertion, the correct answer is that both the assertion and reason are true, and the reason is the correct explanation of the assertion.

### Final Answer:
Both assertion and reason are true, and the reason is the correct explanation of the assertion.

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