题目

Conor Grennan was unwilling to be a volunteer(志愿者). The 29-year-old American was not sure if he had the skills or a strong feeling for it.However, he went to work at an orphanage(孤儿院) in Nepal. His first thought was to make people impressed.I thought that if I volunteered just once. I could retell the story over and over, Grennan said in a Huffington Post article.However, his three-month stay it the orphanage turned into in unusual experience. It was 2004 and Grennan had given up his job to begin a year-long around-the-world trip, His first three months were spent in Nepal.When he 12(xmy)n－10(xny)m的结果是(其中m、n为正整数)(    ) A.　　  2xm－yn　　 　　    　　    　　    B.　　  2xn－ym C.　　  2xmyn　　    　　    　　    　　    D.　　 12xmnyn－10xmnym