If you walk through a park, you may

If you walk through a park, you may enjoy the scents (气味) of flowers, water and soil. If you’re especially lucky, you’ll get to smell fresh-cut grass. It’s a beloved scent that transports many people back to their childhoods. But there’s a dark side to that smell. Indeed, we are in love with the scent of fear. Plants have many different chemical defenses. That smell is one of them, as the grass responds to an attack, signaling (向……示意) to the surrounding grass that danger is coming. The fresh, “green” scent of a just-mowed lawn (刚修剪过的草坪) is the lawn trying to save itself, says a story at science website Real Clear Science. The smell is produced by a mix of chemicals called green leaf volatiles (GLVs，绿叶挥发物). When the leafy plants are injured – by animals eating them, people cutting them, or any other rough (粗鲁的) treatment – they give off GLVs into the air. These GLVs are a warning to neighboring plants that their flowers might be removed, so they can move resources like sugar toward their roots and away from their flowers. This reduces a plant’s potential losses and can help it grow back later. The rush of GLVs does a few other things, too. One chemical helps to close the wound on the damaged plant. Others act as antibiotics (抗生素) and prevent bacterial (细菌的) infections. Some GLVs may also react with animals that eat plants. Silke Allmann and Ian T. Baldwin, researchers from the University of Amsterdam, Netherlands, found that some caterpillars (毛虫) are changed by the GLV compounds (化合物) when they eat a tobacco (烟草) plant. Tobacco makes the caterpillars more attractive to predators (捕食者). For the tobacco plants, this is like having an older brother come to beat up your bully (欺凌者). Thankfully, nothing is coming to eat you when you mow the lawn. Instead, we humans get treated to some great-smelling GLVs. One is a compound known as “cis-3-hexenal”. This is the same chemical that gives strawberries their sweet scent. Similar compounds are also found in apples and olives. “Just about all fresh vegetables have some GLV scents to them,” Baldwin told Live Science, and fruits may release the compounds as they soften. “Throughout evolutionary history, we’ve used that information to know when something is ripe,” Baldwin said. Now we can use it to know when grass is frightened.5. What do we know about GLVs?A. They are harmful to humans.B. They are unique to flowering plants.C. They tend to stay in the air for a long time.D. They are released when plants get hurt.6. How may plants react to the GLVs produced by neighboring plants?A. They grow more quickly.B. They produce more flowers.C. They absorb more water.D. They transport resources to their roots. 7. In Paragraph 5, “an older brother” refers to ______.A. a kind of antibioticB. a predatorC. a caterpillarD. a tobacco plant8. According to Baldwin, GLVs can ______.A. tell us whether fruits are ready to eatB. protect plants from pestC. help fruits grow more quicklyD. help people choose delicious fruits