Assume that there are three transactions T1,T2,T3 that operate (read and write) on the data items A, B, and C. We are using the following notation: RJIX) means that the transaction TJ reads the data item X, while WJ(X) means that the transaction TJ writes on the data item X. You are given the following schedules S1, S2, S3, S4 S1: R2(C), R3(C), W2(C), W1(B), R1(B), W1(C) S2: R2(A), W2(A), W1(C), R3(C), R3(B), W1(B) 53: W2(B), W1(B), W3(B), R2(C), W21A), W2C) S4: R2(C). W2(C), W1(C), W3(A), R1(B), R2(A) Which of those schedules can occur by use of (two-phase locking) 2PL? We assume that the system allows transactions to upgrade shared lock to an exclusive lock, or downgrade exclusive lock to a shared lock. 75 S1 and 3 only S1, 53 and 54 only O S1, S2,S3 and 54 ts @ S3 and 54 only 51 and 52 only TYEYS