Concept:A one-word substitution asks for the exact word that describes the given phrase.Explanation:The phrase means a past time that was happy, peaceful, and ideal.The word Halcyon means calm, peaceful, and idyllically happy.It is often used in the phrase halcyon days.Other options: Cess means a tax or levy; Oracy means skill in speaking; Acumen means sharp judgment.Answer:C. Halcyon