【Couldsmellsaffectyourlifespan？Femalefruitflies（果蝇）withouttheabilitytosmellfoodlivelongerthanotherfruitflies．Thesenseofsmellmaybeconnectedtothecellularageing（细胞老化）processinmanyotherlivingthing】

　　Could smells affect your lifespan？Female fruit flies（果蝇） without the ability to smell food live longer than other fruit flies．The sense of smell may be connected to the cellular ageing （细胞老化） process in many other living things-even people．Such connection has recently been found in both worms and flies．For example，scientists found that removing fruit flies'ability to smell made them live nearly 20percent longer than flies with a sense of smell．

　　They confirmed that food smells were the ones most likely to affect ageing，as nutrition and lifespan are known to be connected in many living things．To test the idea that food smells affect lifespan，they removed flies'ability to smell carbon dioxide，which is produced by some fly foods．They left the rest of the smelling system intact．

　　This action had no effect on male flies，but the females lived 30percent longer than normal．Removing the ability to smell CO2may stop flies getting information about food availability．This could mean that food is not enough，causing processes that encourage flies to survive．Scientists found that the female flies stored extra fat and that both males and females immune（免疫） to CO2were stronger against the stress than normal flies．It is suggested that females may simply be easily influenced by the smells of CO2．

　　Scientists point out that people don't know whether ageing and smell are connected in animals and humans．But they clearly experience physical changes after smelling food．

　　21．From the passage，we learn that what scientists found is to___

　　A．show there is the best way to make lifespan longer

　　B．tell us we should remove our smell ability to live long

　　C．show the sense of smell can affect the cellular ageing process

　　D．explain fruit flies without ability to smell can live longer

　　22．Scientists do some researches to prove___

　　A．the immune system of flies to CO2

　　B．the connections between nutrition and lif