Cette diminution est peut-être attribuable à de nouvelles attentes en matière de services ou à des changements mis en place dans le modèle de services de l'ARC.

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Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
This decrease may be due to evolving service expectations or to changes introduced to the CRA's service model.