题目

器官移植到患者体内，该器官不易成活，从免疫的概念分析，被移植的器官属于：（ ） A．抗原     B．抗体       C．病原体      D．疫苗 答案：A15、Our teacher always urges that the homework _____ in on time, but it doesn’t turn out to be so. A．must hand                                           B．should hand   C．must be handed                     D．be handed