The correct answer is A. Once things are done, there is no need to dwell on them, to worry about them, or to decide who is to blame.
Step-by-step explanation:
In option A, the author uses the same pattern or grammatical structure to present three elements "to dwell... to worry... to decide" because each of these elements includes the preposition "to" and a bare verb. This repetition is known as a parallel structure and makes the sentence to flow naturally. Moreover, the use of parallel structure in this sentence shows the three elements mentioned are equal in terms of importance.