Assertion :- Australian marsupials can be taken as an example of adaptive radiation.
Reason :- A number of marsupials, evolved from an ancestral stock, but all within the Australian island continent.

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 a 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

### Step-by-Step Solution:

1. **Understanding the Assertion**: The assertion states that Australian marsupials are an example of adaptive radiation. Adaptive radiation refers to the process where organisms diversify rapidly into a variety of forms to adapt to different environments.

2. **Understanding the Reason**: The reason provided explains that a number of marsupials evolved from a common ancestral stock, all within the Australian continent. This indicates that these marsupials adapted to various ecological niches available in Australia.

3. **Linking the Assertion and Reason**: Since adaptive radiation involves the evolution of different species from a common ancestor in response to different environmental pressures, the reason supports the assertion. The marsupials evolved into various forms, such as the koala, wombat, and bandicoot, adapting to different habitats within Australia.

4. **Conclusion**: Both the assertion and the reason are true statements. The reason accurately explains why Australian marsupials are an example of adaptive radiation, as they evolved from a single ancestral stock and adapted to various ecological niches.

5. **Final Answer**: Therefore, the correct answer is that both the assertion and reason are true, and the reason is the correct explanation of the assertion.