Final answer:
The correct sentence using a 'how often' adverb is option C: Please arrive before noon, so we have time to warm up.
Step-by-step explanation:
The correct sentence using a "how often" adverb is option C: Please arrive before noon, so we have time to warm up. The phrase "before noon" describes how often the action of arriving should happen. It is an adverbial phrase answering the question "How often should you arrive?".
Learn more about Adverbs