题目

He failed the college entrance exam last year, whichd his parents. As you know, they used to think highly of him. 答案：【1】disappointed20．下列属于人体免疫第三道防线的是（　　）A．免疫器官和免疫细胞B．皮肤和黏膜C．吞噬细胞和免疫器官D．体液中的杀菌物质和吞噬细胞