Flies(苍蝇) are one of the most dangerous enemies of human. They are dangerous because they carry diseases(疾病) , Flies do not care whether the food they eat is d{#blank#}1{#/blank#}or clean. The food they like best is o{#blank#}2{#/blank#}the dirtiest that can be found. Then they may f{#blank#}3{#/blank#}into a house where good clean food is kept and begin to walk all over it and eat it. Soon the good clean food becomes unfit(不合适) for people to eat. Often a person who is preparing f{#blank#}4{#/blank#}does not realize that it is unfit for people to eat, so the food is put on the t{#blank#}5{#/blank#}and eaten. Those who eat such food become dangerously ill. That's why we must get rid of(消灭) flies.