Cockroaches（蟑螂）arethemostunpleasantofallinsects．Seeminglylargeandfast，andtheyliveinthemostdisgustingconditions．It'snowonderthefirstreactionofmanytoseeingacockroachistotrytodestroyit，andfewwoulddrop

　　Cockroaches（蟑螂） are the most unpleasant of all insects．Seemingly large and fast，and they live in the most disgusting conditions．

　　It's no wonder the first reaction of many to seeing a cockroach is to try to destroy it，and few would drop a tear at the thought of the entire species dying out．

　　But，of course，things are not so simple．Unpleasant though they are，according to biologists the ill-famed cockroach is essential to the survival of the planet's delicate ecosystem．

　　According to Srini Kambhampati，professor and chairman of the biology department at the University of Texas，the disappearance of cockroaches would play havoc with the nitrogen cycle．

　　As a leading expert on roaches，he said："Most cockroaches feed on rotten organic matter，which traps a lot of nitrogen．Cockroach feeding has the effect of releasing that nitrogen （in their waste）which then gets into the soil and is used by plants．In other words，extinction of cockroaches would have a big impact on forest health and therefore indirectly on all the species that live there．"

　　The professor also warned that the Earth's 5，000to 10，000cockroach species are also an important source of food for many birds and small mammals like mice and rats．

　　In turn，thesekillers themselves are food of many other species like cats，wolves and snakes，as well as eagles and other big birds．

　　Any cut to the number of cockroaches would thus have a harmful effect on the wellbeing of all these species that could have a destroying effect on wildlife across that world．

　　Of course，there's not much chance of a cockroach extinction level event happening any time soon．Still，although it was once believed that they would be one of the few creatures to survive even a nuclear Third World War，that idea has since been considered untrue．

　　28．What is the main idea of this passage？___

　　A．The hated cockroach is essential to the survival of the planet's delicate e