Explanation:

- Mr. A meets Mr. B.

This introduces A and B, but their relationship is not clear.

- B is the father of a son C and a daughter D.

This establishes B as the father of C and D.

- E is the mother of A.

This indicates that E has a child, A, but does not clarify A's relation to B directly.

- C is married and has one son.

This provides information about C’s family.

- E is the daughter-in-law of B.

Since E is married to B's child, A (E's child) must be B's grandson.

- How is A related to B?

Based on the relationship chain, A is B's grandson.

- Options to choose from:

1. Uncle

2. Grandson

3. Son

4. Nephew

- Given the explanation, the correct answer is: Option 2: Grandson