Le plafond de la phase I doit être fixé à un niveau atteignable non seulement par les technologies de réduction du mercure existantes, mais aussi par les technologies émergentes.

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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.
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The Phase I cap should be set at a level that could be met with current as well as emerging mercury control technology.