【正确答案】 D

【答案解析】[解析] “主语+must +have+过去分词”结构，表示对过去事实的推测。例如：The road is wet. It must have rained last night. (路是湿的，昨晚肯定下雨了。)．I didn't hear the phone. I must have been asleep. (我没有听见电话铃响，我肯定是睡着了。)