A、It is damaged by extremely dry weather. B、It loses water to stronger trees. C、Insects destroy the tree’ s bark. D、Certain beet

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.
Now listen to the following recording and answer questions 16 to 18.
16. What is causing the death of the infected elm trees?
17. According to the speaker, what causes the healthy elm tree to become weak?
18. According to the speaker, how do experts hope to limit the spread of the disease in the future?