Consider a Simple Checkpointing Protocol and the following set of operations in the log.(start, T4); (write, T4, y, 2, 3); (start, T1); (commit, T4); (write, T1, z, 5, 7); (Checkpoint);(start, T2); (write, T2, x, 1, 9); (commit, T2); start, T3); (write, T3, z, 7, 2); if a crash happens now and the system tries to recover using both undo and redo operations, what are the contents of the undo list and the redo list?

• A. Undo : T3, T1; Redo T2
• B. Undo : T3, T1; Redo T2, T4
• C. Undo : none; Redo T2, T4, T3, T1
• D. Undo : T3, T1, T4; Redo T2