If a patient should take a medication at bedtime, which abbreviation should be used?

The abbreviation "qhs" stands for "quaque hora somni," which translates to "every night at bedtime." This is the correct choice for indicating that a medication should be taken at bedtime. It clearly specifies the timing of the medication in relation to the sleep period, ensuring that patients or caregivers understand the intent for administering the medication at night.

The other abbreviations serve different purposes in medication administration. "Ac" means "before meals," which clearly is not relevant for a bedtime dosage. "Pc" indicates "after meals," which again is not applicable for medications intended for bedtime. "Stat," meaning "immediately," is used for urgent medications that need to be administered without delay and does not relate to timing associated with meals or sleep. Thus, "qhs" is the most appropriate abbreviation for a medication that should be taken at bedtime.