【正确答案】 D

【答案解析】解析：mystery n.神秘：神秘的事物(如：Her mystery makes her charming．His sudden disappearance still remains a mystery．)。myth n．神话：虚构的信念(理论)。depression n．抑郁，沮丧；不景气，萧条(期)。pessimism n．悲观(主义)。