单选题 It is naive to expect that any society can resolve all the social problems it is faced with ______.
A. for long B. in and out C. once for all D. by nature

【正确答案】 C

【答案解析】[解析] C项once for all意为“一劳永逸’’；A项for long意为“长久”；B项in and out意为“里外”；D项by nature意为“本质上”。