Assertion : In woody stems, the amount of heartwood continues year after year.
Reason: The cambial activity continues uninterrupted.

Options

A. If both A and R are true and R is the correct explanation of A
B. If both A and R are true but R is not the correct explanation of A
C. If A is true and R is false
D. If both A and R are false

Answer

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that "In woody stems, the amount of heartwood continues year after year." This means that as time passes, the heartwood, which is the inner part of the wood, increases in quantity.

2. **Understanding the Reason**:
- The reason provided is "The cambial activity continues uninterrupted." The cambium is a layer of actively dividing cells that contributes to the secondary growth in plants, leading to the formation of new wood layers.

3. **Formation of Heartwood**:
- Heartwood is formed from the secondary xylem that becomes non-functional over time. As the tree grows, older layers of xylem (the sapwood) become heartwood, which is essentially the inner part of the wood that no longer conducts water.

4. **Role of Cambium**:
- The cambium layer is responsible for the production of new xylem and phloem. As the cambium continues to divide, it adds new layers of sapwood. Over time, these layers of sapwood become heartwood as they age and lose their functionality.

5. **Conclusion**:
- Since both the assertion (the amount of heartwood increases year after year) and the reason (the cambial activity continues uninterrupted) are true, and the reason correctly explains the assertion, we conclude that both statements are true and the reason is the correct explanation of the assertion.

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

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