Based on the passage excerpt, the person or the people that were most tired the next day is the "Darius's army."
This is because the Darius Army didn't sleep through the night, thereby making them have fatigue and tired the next day.
This is evident when the passage includes, "Darius, on the other hand,
Darius, on the other hand,mindful of Alexander's unpredictable maneuvers, ordered his army to stand to throughout the night in readiness for a surprise attack."
Hence, in this case, it is concluded that the correct answer is option A. "Darius's army."
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