test applied cource

Question

Consider the following order of transactions:
T2: R(y); T3:W(y); T3: commit; T1: W(y); T1: commit; T2: R(x); T2: W(z); T2: commit; T4: R(y);T4: R(x); T4: commit.

Let the above schedule be S, if S is serializable, then how many conflict serial orderings of S is possible?___________

A). 1

B). 2

C). 3

D). None

Comments

$2$

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How ?