Concept:The question asks for one word that means a past time remembered as happy and peaceful.Explanation:Check the meaning of each option.Cess means a tax or levy.Oracy means skill in speaking.Halcyon means idyllically calm, peaceful, and happy, especially about a past period.Acumen means sharp judgment or insight.Thus, Halcyon perfectly matches the given expression.Answer:Halcyon (Option C).