单选题     What's the best way to protect a tender, green seedling from the hungry stomach of deer? Give the seedling bad breath!
    The same chemical that gives people bad breath after they have eaten garlic can save small trees from being eaten by animals.
    A kind of chemical selenium (硒), which is also found in garlic, is planted in the soil near a young tree. The tree's roots absorb the selenium which is then carried to the leaves.
    From there the selenium is used to form a chemical called dimethyl selenide (乙烷硒化物)—the same chemical made in the human mouth after eating garlic. As deer wander around looking for food, they smell the seedlings' leaves and leave the plants alone.
    The selenium is important. Why? Because each year deer eat millions of dollars' worth of trees farm seedlings.
    So far, selenium has been tested only on Douglas fir (枞树) seedlings, but researchers think they could protect fruit trees and garden plants, too.

单选题     When people eat garlic, ______.

单选题     According to this passage the bad smell given off from those leaves is that of ______.

单选题     Up till the time the news was announced, this kind of chemical was used ______.

单选题     The best title of this passage is ______.