屋顶的面积很大，大气压对屋顶有很大的压力，但并没有把屋顶压塌，这是因为：                                                          （   ）

    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．

材料一：30岁左右便收徒讲学，前后从事教育四十多年。相传他有弟子3000人，其中出名的有72人。他提倡“道之以德，齐之以礼”，主张“为政以德”。他有关教育思想和教育方法的许多言论，成为后世传颂的格言。

材料二：他生活在战国末期，是荀子的学生。他强调“法治”，并提出“事在四方，要在中央；圣人执要，四方来效”的理论。