Correct : a

The correct answer is Option A — Both T1 and T2 only read A.
In database concurrency control, two operations from different transactions on the same data object are said to conflict if and only if at least one of the operations is a Write. This gives three conflicting pairs and one non-conflicting pair on any shared data item A.
The three conflicting pairs are: Read-Write (one transaction reads while the other writes), Write-Read (one writes while the other reads), and Write-Write (both transactions write). In all these cases, the order of execution can affect the final outcome or the value read, which is why they conflict.
The only non-conflicting pair is Read-Read — when both transactions only read A, neither modifies it, so the order of their execution has no effect on the database state or on what either transaction reads. This is Option A.
Option B (T1 reads, T2 writes): A Read-Write conflict — the value T1 reads depends on whether T2''s write happens before or after. Conflict exists. Incorrect.
Option C (T1 writes, T2 reads): A Write-Read conflict — the value T2 reads depends on whether T1''s write has already occurred. Conflict exists. Incorrect.
Option D (Both write): A Write-Write conflict — the final value of A depends on which write happens last. Conflict exists. Incorrect.
The fundamental rule to remember: two reads never conflict; any operation involving a write can conflict with any other operation on the same data item.