Definition: Idempotence is the property of certain operations in mathematics and computer science whereby they can be applied multiple times without changing the result beyond the initial application.
Performing Commit Again and again will not change the initial result.
For example: W(A) → Commit → Commit and repeat…. the result will remain same, there is not even slight possibility that result can change anytime on its own using commit only.
So, Answer is (A)
Now, can Write change the result? Yes there is possibility that the initial result gets changed.
For example: Initially A=1000 then we write A=500 using W(A) → W(A) → W(A) and repeat…. since there is slight possibility that result is changed by W(A) we will not consider it as answer.
So, C is wrong.
and B and D are obviously wrong since they can change value/result