Any question" places a strict limit on the number of questions allowable to exactly one. For example, there was exactly one question as to who wore the pants. However, where the number of questions has not been determined, or is unrestricted, then the plural should be used.
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Explanation:
Any question" places a strict limit on the number of questions allowable to exactly one. For example, there was exactly one question as to who wore the pants. However, where the number of questions has not been determined, or is unrestricted, then the plural should be used.