题目

 阅读理解。 Canadians like to say Thank you when others help them or say something kind to them. People of many other countries do so, too. It's a very good habit. You should say Thank you when someone passes you the salt on the table, or opens the door for you, or says you have done your work well. Thank you is used not only between friends but also between parents and children, brothers and sisters, husbands and wives. Excuse me is another useful short expression. When you hear someone say so behind you, you know somebody wants to walk past without touching you. It's not po2、2009年9月，由北京科兴生物制品有限公司生产的甲型H1N1流感病毒（一种RNA病毒）裂解疫苗获得国家食品药品监督管理局颁发的药品批准文号，疫苗投入使用。全球首支获得药品批准文号的甲型H1N1流感疫苗由此诞生。下列有关甲流感病毒及疫苗的叙述中，不正确的是 A．甲流病毒容易发生基因突变，所以甲流疫苗难以制备 B．感染“甲流病毒”后，人体参与免疫的细胞主要是B淋巴细胞 C．少数人接种甲流疫苗后出现过敏症状的原因是自身免疫功能过强 D．甲流病毒在宿主细胞内的增殖过程中要遵循碱基互补配对原则