【正确答案】 A

【答案解析】[听力原文] Good evening, I am Steve Johnson and I represent the American Elm Society. Today I'd like to introduce you to some of the problems faced by elm trees. Many of you are familiar with this huge tree. It's found in many areas of US and Canada in cities and small towns. Well, as you may know, the American elm has been threatened by a dangerous disease. The disease is caused by a fungus, when that fungus infects the tree, it blocks the circulation of water inside the tree. As a result, the tree cells don't receive water and without water, of course they can't survive. The tree's leaves become dry, fall off, and eventually the tree dies. You may be interested in how the disease is transmitted, well, a very small insect called elm bug beetle brings the fungus with it. The beetle uses the tree to reproduce itself. The female builds channels in the wood for the eggs, at the same time, it infects the tree with fungus. The worst thing is that the process seems unstoppable, because once the beetle leaves the infected tree it carries the fungus on its body and poisons a healthy tree. Of course, we are trying to fight the disease, in the past, infected trees were simply cut down. That method reduces the number of the infected trees but it never stop the disease. Now experts are trying to get to the root of the problem, they are working on ways to control the beetle that spreads the disease. What is causing the death of the infected elm trees? 细节题。根据The disease is caused by a fungus, when that fungus infects the tree, it blocks the circulation of water inside the tree. As a result, the tree cells don't receive water and without water, of course they can't survive. 可知水分无法循环造成了榆木的死亡。因此，正确答案是A。

【正确答案】 D

【答案解析】[听力原文] According to the speaker, what causes the healthy elm tree to become weak? 细节题。根据You may be interested in how the disease is transmitted, well, a very small insect called elm bug beetle brings the fungus with it. 可知榆树的疾病是由一种小昆虫传播的。因此，正确答案是D。

【正确答案】 A

【答案解析】[听力原文] According to the speaker, how do experts hope to limit the spread of the disease in the future? 细节题。根据Now experts are trying to get to the root of the problem, they are working on ways to control the beetle that spreads the disease. 可知科学家们要从根源上控制传播疾病的虫子。因此，正确答案是A。