Assertion : All Eutherian are placental mammals .
Reason : All placental mammals have menstrual cycle

Options

A. If both Assertion & Reason are True & the Reason is a correct explanation of the Assertion .
B. If both Assertion & Reason are True but Reason is not a correct explanation of the Assertion.
C. If Assertion is True but the Reason is False .
D. If both Assertion & Reason are False.

Answer

To solve the question, we need to analyze both the assertion and the reason provided.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that "All Eutherians are placental mammals."
- Eutherians (also known as placental mammals) are indeed characterized by the presence of a placenta, which allows for a more complex and prolonged gestation period compared to other mammals.

2. **Evaluating the Reason**:
- The reason states that "All placental mammals have a menstrual cycle."
- This statement is not entirely accurate. While many placental mammals do have a menstrual cycle, there are also some that exhibit an estrous cycle instead. For example, dogs are placental mammals but they have an estrous cycle, which includes a heat period rather than a menstrual cycle.

3. **Conclusion**:
- Since the assertion is true (all Eutherians are indeed placental mammals), but the reason is false (not all placental mammals have a menstrual cycle), we conclude that the assertion is true while the reason is false.

4. **Final Answer**:
- The correct answer is that the assertion is true but the reason is false.