题目

黏膜具有阻挡病原体的作用，呼吸道和消化道的黏膜还能分泌杀菌物质。它们属于特异性免疫。 答案：错 【解析】 试题分析：人体的三道防线：第一道防线是皮肤和黏膜，它们不仅能阻挡病原体侵入人体，而且它们的分泌物还有杀菌作用，人体的第二道防线指的是体液中的杀菌物质和吞噬细胞，体液中含有的一些杀菌物质能破坏多种病菌的细胞壁，使病菌溶解而死亡，吞噬细胞能吞噬和消灭侵入人体在下列各句的空白处填入一个适当的词, 使句子意思表达完整， 语法正确。 【1】 Teachers always tell students to arrive on _________ for school every day. 【2】 As we know, dogs are our friends because they are __________ of friendly and smart.【3】 Elephants can walk for a long time and never get ________. They can remember places.【4】 My brother is _________ on the phone to his cousin about his family and delicious food .【5】Today, people down many trees. So many animals are in danger.