2016年英语四级考试模考强化实战训练题五_第2页

　　Part II Reading Comprehension (Skimming and Scanning) (15minutes)

　　To Save Trees, Fighting One Alien Insect with Others

　　Rusty rhea sighs wistfully as he talks about the beauty and peace of standing amid a grove (小树林) of deep green hemlocks in cet4v.com of them up to 160 feet (50 meters) tall and more than 500 years old.

　　"This is a very special tree," said Rhea, an entomologist for the U.S. Forest Service's Forest Health Protection program in Asheville, North Carolina, "I was brought up here, and I don't want to see another species go by the wayside."

　　The evergreen trees, a hallmark of southern Appalachia's national parks, are under attack by an invasive inse4ct barely visible to the eye but potent enough to fell the giants of the eastern United States' old-growth forests.

　　Already the tiny bug from Japan, known as the hemlock woolly adelgid (HWA), has killed upward of 95 percent of the hemlocks in Virginia's Shenandoah National Park. Now they are making their way through the half-million-plus-acre (200,000-plus-hectare) Great Smoky Mountains National Park in North Carolina and Tennessee.

　　The hemlocks shade streams, keeping water temperatures just right for brook trout (鲑鱼) and other fish. They also house birds such as the black-throated green warbler, solitary vireo, and northern goshawk, all three of which mainly shelter in stands of hemlock trees.

　　Because of the insect's broad impact on the entire ecosystem of southern Appalachia, HWA stands to cause wider damage than the American chestnut blight (枯萎病)of the early 1900s. That fungus from Europe killed off the once dominant chestnut trees from the northeast United States cet4v.com Appalachian Mountains.

　　In addition, a species related to HWA, the balsam woolly adelgid, has already killed about 90 percent of the mature Fraser fir trees in the Smokies.

　　Acting Quickly

　　HWA arrived in the U.S. Pacific Northwest via nursery plants from Japan in 1924. By 1951 the tiny invader had been found in Virginia. Since then the insect has spread to more than 15 U.S. states.

　　The key to killing the HWA is to catch it early and act quickly. It's already well established in the Great Smoky Mountains, where Rhea and others are trying to stem the spread of the bugs.

　　HWA multiply quickly: All of the insects are females that reproduce asexually (无性地), laying several hundred eggs a year. cet4v.com to the nymph, or crawler, stage, they are dormant from about June until October, after which they emerge and establish themselves on trees.

　　Winds and birds and other animals spread the crawlers through the forest.

　　HWA crawlers feed on the new growth of hemlocks by piercing the twigs that hold the branches, sucking the sap, and injecting toxic saliva. The needles turn from a deep green to a grayish green and eventually die, depriving the tree of nutrition from photosynthesis.

　　An infected tree usually dies within five years of initial attack. Infection is signaled by either a white, cottonlike material that appears along a tree's twigs or by the "baldness" of a tree's upper branches.

　　Plans of Attack

　　In the Pacific Northwest the hemlocks seem to be tolerant of the creatures' feeding, and in the cold northeast, winters seem to keep them at bay. But in the warm southeast, with weather approximating that of the insects' native Asian homes, they thrive.

　　Chemical sprays-such as insecticidal soaps and horticultural oils as well as trunk or soil injections-have helped to kill some of the HWA infestations.

　　But spraying must be repeated every six months, and injections are expensive and last only two years at most. These methods can't be used conveniently or safely in remote areas or near the streams where hemlocks grow thickly.

　　Long term, the best way to control the pests appears to be releasing other insects that feed exclusively on HWA. Scientists have studied HWA in Japan and China and identified three such species. One of them, the Sasajiscymnus tsugae (St) beetle, was released in areas of Great Smoky Mountains National Park in 2002.

　　Studying what controls a species in its native habitat-including climate, pr

　　edators, and host resistance-provided clues about which insects to use against HWA, said Kristine Johnson. Based in Gatlinburg, Tennessee, Johnson is a supervisory forester for Great Smoky Mountains National Park.

　　"Biological control is the only long-term hope to save the trees in the backcountry (穷乡僻壤)," she said. "We have 800 square miles (2,100 square kilometers) of contiguous wilderness. We value the native forest, and it's entirely worth defending."

　　Risky Business

　　Releasing one species of non-native bug to kill another could be risky business, potentially creating another type of infestation. But scientists first quarantined and studied the HWA-killer insects.

　　They believe the St beetles are the best answer to the HWA problem and that they won't cause side damage. This tiny black female beetle, the size of a poppy seed, is already spreading in the Great Smoky Mountains.

　　But the beetle and other HWA-killer insects are seasonal, so it will take several different ones operating year-round to keep HWA in check, Rhea said. He doesn't believe HWA will be completely eradicated (根除) but will instead be kept in balance by the predator insects. "We're trying to insert a balance in a system that's out of balance," he said.

　　Each St beetle can lay 200 to 300 eggs, said Ernest Bernard, professor of entomology at the University of Tennessee in Knoxville.

　　Bernard's laboratory is one of several that are breeding the beetles.

　　"Each beetle eats hundreds of baby adelgids a year," he said. And about 120,000 of the beetles have been released in the past couple years in the Smokies, but it is still too early to measure their impact.

　　One good sign, Bernard said, is that some beetle larvae (幼虫) have been found in areas where they were not released, indicating that the HWA killers may be reproducing and spreading.

　　1. The passage gives a general description of an invasive insect, HWA.

　　2. Hemlock is a hallmark of southern Appalachia's national parks.

　　3. The invasive insect, known as the hemlock woolly adelgid (HWA), is from Japan.

　　4. The key to killing the HWA is to catch it early and act quickly.

　　5. An infected tree usually dies immediately.

　　6. The Hemlock in the U.S. will be saved from HWA soon.

　　7. The long term, best way to control the pests HWA is spraying.

　　8. Since 1951 the HWA has spread to more than________.

　　9. Releasing one species of non-native bug to kill another could create________.

　　10. It will take several different insects operating year-round to________.

　　Part II Reading Comprehension (Skimming and Scanning)

　　1. N 结合标题To Save Trees, Fighting One Alien Insect with Others迅速扫读全文可知，文章主要不是描写HWA这种虫害本身，而是如何防治这种虫害，故题干表述不正确。

　　2. Y 根据题干中的信息词hallmark和Appalachia's national parks定位原文，第三段明确指出The evergreen trees, a hallmark of southern Appalachia's national parks...，可知题干表述正确。

　　3. Y 根据题干中的信息词HWA定位原文，第四段有Already the tiny bug from Japan, known as the hemlock woolly adelgid (HWA)...，可知题干表述正确。

　　4. Y 题干中有acting quickly, 与一小标题同，估计答案在其下段落下。定位到第二段，发现题干是文中原句，故题干表述正确。

　　5. N 根据题干中的信息词An infected tree定位原文，在Acting Quickly下的倒数第二段段末有An infected tree usually dies within five years of initial attack，可知题干表述错误。

　　6. NG 文章后半部分讲到为了控制HWA，美国已在受灾部分地区投放HWA的天敌St bettles，但是在文章倒数第二段末尾指出这种方法是否有效还无法判断(too early to measure their impact)，故本题表述正确与否末可知。

　　7. N 在对抗HWA的方法中，文章着重介绍了引入其天敌来达到生态平衡的方法，且在Plans of Attack下的第四段段首有明确说明，故题干表述错误。

　　8. 15 U.S. states。根据题干中的信息词1951定位原文，在Acting Quickly下第一段可找到答案。

　　9. another type of infestation。读完原文，发现Risky Business下讲了用St bettles来控制HWA这种方法可能带来的风险，而题干正是谈的这种方法，定位Risky Business下的段落，首段即可找到答案。

　　10. keep HWA in check。最后一题多出现在文章末尾，根据题干中的信息词year-round定位Risky Busines下的段落，在第三段第一句可以找到答案。