完形填空。 People often fall ill because of me__1__,they can hardly blame me;it is largely their own__2__

     People often fall ill because of me__1__,they can hardly blame me;it is largely their own__2__.
A tired person may get__3__specially when he goes to crowded places with polluted air.A
sudden change in__4__is another factor.In hot summer,people turn on the air-conditioner upon
returning home.They will catch a cold easily.
     My latest victim is an energetic student.After school,he played football hard for two hours.
Though__5__,he still went to the cinema.Then he got back home and took a cold shower
immediately.
     I seized this golden chance to__6__him.He reacted,trying to__7__me,but I was already__8__
deep in his throat.He kept sneezing(打喷嚏)and his nose was running,__9__he put on some
warm clothes,it didn't work,for there were too many of us.Besides,his sore throat kept__10__
him,and he developed a cough to force me and my family out,but__11__.
     The next day he couldn't go to__12__.He had lost his appetite and was not as__13__as
before.His mother made him orange juice every few hours for more vitamin C,which would help
his__14__.
     For two days he was__15__y his mother.As he rested more,his defense strengthened and I
began to feel the__16__.I knew I had to__17__him before long.But I am not the one who gives
up easily,and I made everyeffort to fight back.__18__,it was my turn to feel__19__now,for his
defense system was starting an all out attack against me.I  became__20__and finally my time
was over.
     Do you know what I am?