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．

以下是我国经济重心变化示意图，与这三幅图相对应的大致时期依次是(   )

探究力对原来静止的物体做的功与物体获得的速度变化的关系，实验装置如图所示，实验主要过程如下：

⑴设法让橡皮筋对小车做的功分别为W、2W、3W

⑵分析打点计时器打出的纸带，求出小车的速度v₁、v₂、v₃…；

⑶作出W﹣v草图；

⑷分析W﹣v图象，如果W﹣v图象是一条直线，表明w∝v；如果不是直线，可考虑是否存在w∝v₂、w∝v₃等关系．

以下关于该实验的说法中有一项不正确，它是