患过麻疹以后不再患该病是因为（ ）。
A．吞噬细胞可随时吞噬麻疹病毒
B．麻疹病毒不会再感染人体
C．麻疹病毒可长期存在于人体内
D．人体产生的抗体可长期在人体内存留
答案：D
分析：人之所以能够在具有许多病原体的环境中健康的生存，是因为人体具有保卫自身的三道防线；人体的第三道防线由免疫器官和免疫细胞（主要是淋巴细胞）组成，当病原体进入人体后，会刺激淋巴细胞产生一种抵抗该病原体的特殊蛋白质，叫做抗体，抗体能够帮助人体清除或灭杀进入人体的病原体．
解答：解：得过麻疹的人，体内已经产生了抵抗麻疹病毒的抗体，并且这种抗体等人病好后仍然会存留在人体内，当麻疹病毒再次进入人体后，原先已有的抵抗麻疹病毒的抗体就会将其消灭，因此得过麻疹的人以后不再得麻疹，因为人体产生的抗体可长期在人体内存留．
故选：D
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| I am Zhang Yu. I am a student in Yuxin Middle School. My _1_ is very big. There are about 3, 000 _2_ in our school, and we have lessons (上课) in different _3_ . There is a tall building near the school gate. The _5_ and the teachers' offices are in the same building. There is a _5_ behind the building. We can borrow (借) _6_ from it. Next to the library is our science lab. We have _7_ lessons in it. We have a gym _8_ our school, and it is behind the science lab. There are _9_ trees and flowers in our school. Our school _10_ nice. We like it very much. | ||||