Passage FourWhat's the best way to protect a tender, green seedl

Passage FourWhat'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.А kіnd оf сhеmісаl ѕеlеnіum（硒）, whісh іѕ аlѕо fоund іn gаrlіс, іѕ рlаntеd іn thе ѕоіl 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.Up till the time the news was announced, this kind of chemical was used_____.
A、all over the world
B、all over the United States
C、on fruit trees and garden trees
D、on Douglas fir young trees
【正确答案】：D
【题目解析】：参考文章最后一段。