题目内容：

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 20 percent longer than flies with a sense of smell．

They confirmed that food smells were the ones most likely to affect ageing, as nutrition (营养) 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．

This action had no effect on male flies, but the females lived 30 percent longer than normal．Removing the ability to smell CO2 may 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 from stored extra fat and that both males and females immune (免疫) to CO2 were 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．

1.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

2.Scientists do some research to prove

A. the immune system of flies to CO2

B. the connections between nutrition and lifespan

C. the importance of food smells to our humans

D. the connections between food smells and lifespan

3.According to scientists' opinion, we can see that ________．

A. flies without ability to smell is encouraged to store extra energy

B. male flies in general can live longer than female ones

C. both male and female flies can live longer without the ability to smell

D. flies without ability to smell can also get information about food availability

4.Which of the following best describes the passage as a whole?

A. CO2 has few effects on female flies．

B. The sense of smell might have an effect on living things．

C. The sense of smell is necessary to humans' health．

D. Female fruit flies can always live longer than male flies．