【正确答案】 C

【答案解析】[解析] leave后面可以跟带现在分词、过去分词、不定式、形容词、介词短语的复合结构以及其他情况，如：Don’t leave her waiting．It’s better to leave some things unsaid．I’ll leave you to settle the business．His illness has left him weak．I’ll leave it to you to buy the tickets/leave buying the tickets to you．本题的leave后面跟的是带过去分词的复合结构。由于宾语太长(后面有定语)，将过去分词undone提到宾语things的前面了。