[A] : Haversian canals are inter connecting canals that run usually longitudinally through dense bone of vertebrates.
[R]: They contain nerves and blood. Each canal serving a series of concentric Iamellae

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 "Haversian canals are interconnecting canals that run usually longitudinally through dense bone of vertebrates."
- This means that within the dense bone structure, there are canals (Haversian canals) that run along the length of the bone.

2. **Understanding the Reason**:
- The reason states that "They contain nerves and blood. Each canal serving a series of concentric lamellae."
- This indicates that these Haversian canals are not just hollow tubes; they contain essential components such as blood vessels and nerves, and they are surrounded by concentric layers of bone matrix called lamellae.

3. **Analyzing the Truth of Each Statement**:
- **Assertion**: True. Haversian canals are indeed found in the dense bone of vertebrates and run longitudinally.
- **Reason**: True. Haversian canals do contain blood vessels and nerves, and they are associated with concentric lamellae.

4. **Evaluating the Relationship Between Assertion and Reason**:
- While both statements are true, the reason does not directly explain why Haversian canals are interconnecting canals that run longitudinally. The reason provides additional information about the contents of the canals and their structural relationship to lamellae but does not clarify the assertion itself.

5. **Conclusion**:
- Therefore, the correct answer is that both the assertion and reason are true, but the reason is not the correct explanation of the assertion.

### Final Answer:
- Both assertion and reason are true, but the reason is not the correct explanation of the assertion.

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