[A]: Smoking causes cancer of tongue, lips & lungs.
[R]: It inactivates P 53 genes

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 (A)**:
- The assertion states that "Smoking causes cancer of the tongue, lips, and lungs."
- This is true as smoking is known to introduce carcinogenic substances into the body, which can lead to the development of cancer in these areas.

2. **Understanding the Reason (R)**:
- The reason provided is that "It inactivates P53 genes."
- The P53 gene is crucial for regulating the cell cycle and preventing tumor formation. When this gene is inactivated, it fails to control cell division properly, leading to uncontrolled growth, which can result in cancer.

3. **Linking Assertion and Reason**:
- The assertion is true because smoking introduces carcinogens that can lead to cancer.
- The reason is also true because the inactivation of P53 genes by these carcinogens contributes to the development of cancer by allowing uncontrolled cell division.

4. **Evaluating the Relationship**:
- Since both the assertion and the reason are true, and the reason provides a correct explanation for the assertion, we conclude that the assertion is supported by the reason.

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