Concept:Use constraints to deduce seating positions in a row.
Explanation:Four seats in a row (positions 1,2,3,4).
Condition 1: A is next to B.
Condition 2: A is not next to C.
Condition 3: C is not next to D.
Consider A and B at positions (2,3).
• If seat 2 = A, seat 3 = B, then remaining seats 1 and 4 for C and D.
A's neighbors: seats 1 and 3. To avoid A next to C, C cannot be at seat 1. So C at seat 4, D at seat 1.
Check: C (seat 4) not next to D (seat 1) — satisfied. D's only neighbor is seat 2 (A).
• If seat 2 = B, seat 3 = A, then similarly C at seat 1, D at seat 4. D's neighbor is seat 3 (A).
Other placements (A,B at ends) violate condition 3.
Thus in all valid arrangements, D is adjacent to A.
Answer:D is next to A, so the correct option is A.