Final answer:
The dash in the sentence is used to set off further detail or explanation.
Step-by-step explanation:
The dash in the sentence “There was not a moment to lose for the rider or for the horse” is used to set off further detail or explanation. It is used to provide additional information about the lack of time for both the rider and the horse. The dash separates the main clause from the clause that explains why there was no time to waste.
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