[解析]
(1)B.词义猜测题。根据划线词前文When a germ gets inside your body and meets its match,that B cell becomes active.(当一个细菌进入你的身体,遇到它的对手,B细胞变得活跃)和后文thousands of B cells create"antibodies",which attach to the germ and destroy it.(成干上万的B细胞产生"抗体",附着在细菌上并摧毁它)可知,B细胞进行自我复制,变成成干上万个来摧毁细菌。所以replicates为"复制"之意。A.Repairs修理;B.Reproduces复制;C.Replaces代替;D.Recycles回收。故选B。
(2)B.细节理解题。根据第三段At the height of the battle,B cells can make thousands of antibodies(抗体)in a second.That's when you start feeling better.(在战斗最激烈的时候,B细胞可以在一秒钟内产生数干个抗体。那是你开始感觉好些的时候)可知,在抗体达到顶峰的时候,你开始感觉好些。故选B。
(3)D.推理判断题。根据第四段Vaccines contain dead or weakened germs that let your body make memory B cells.(疫苗中含有死亡或弱化的细菌,可以让你的身体产生记忆B细胞)可推断,疫苗可以让你的身体产生记忆B细胞。故选D。
(4)C.标题判断题。根据文章第一段But they prevent you from getting sick.How?By teaching your body how to fight germs(病菌).Some vaccines(疫苗)contain germs of a specific disease that have either been killed or weakened,so the shots won't give you the disease.(但它们能防止你生病。如何?通过教会你的身体如何对抗细菌。一些疫苗含有某种特定疾病的细菌,这些细菌要么被杀死,要么被削弱,所以这种疫苗不会让你得病)以及全文内容可知,文章主要讲述了疫苗是如何帮助身体消灭病菌的。所以How Vaccines Work(疫苗如何工作的)作为文章标题最为合适。故选C。