综合写作23
Reading
Populations of the yellow cedar, a species of tree that is common in northwestern North America, have been steadily declining for more than a century now, since about 1880. Scientists have advanced several hypotheses explain this decline.
One hypothesis is that the yellow cedar decline may be caused by insect parasites, specifically the cedar bark beetle. This beetle is known to attack cedar trees; the beetle larvae eat the wood. There have been recorded instances of sustained beetle attacks overwhelming and killing yellow cedars, so this insect is a good candidate for the cause of the tree’s decline.
A second hypothesis attributes the decline to brown bears. Bears sometimes claw at the cedars in order to eat the tree bark, which has a high sugar content. In fact, the cedar bark can contain as much sugar as the wild berries that are a staple of the bears’ diet. Although the bears’ clawing is unlikely to destroy trees by itself, their aggressive feeding habits may critically weaken enough trees to be responsible for the decline.
The third hypothesis states that gradual changes of climate may be to blame. Over the last hundred years, the patterns of seasonal as well as day-to-day temperatures have changed in northwestern North America. These changes have affected the root systems of the yellow cedar trees: the fine surface roots now start growing in the late winter rather than in the early spring. The change in the timing of root growth may have significant consequences. Growing roots are sensitive and are therefore likely to suffer damage from partial freezing on cold winter nights. This frozen root damage may be capable of undermining the health of the whole tree, eventually killing it.
Listening
Unfortunately, we still don’t know what’s killing the yellow cedar, none of the explanations discussed in the reading is adequate.
First, the cedar bark beetle. Well, the problem with this explanation is that healthy yellow cedars are generally much more resistant to insect infestation than other tree species. For example, the bark and leaves of yellow cedar are saturated with powerful chemicals that are poisonous to insects. So, healthy cedars are unlikely to suffer from insect damage. So, how can we explain those dead cedars that were infested with beetles. In those cases, the beetles attack trees that were already damaged or sick, and would’ve probably died anyway. So, the beetles are not the fundamental cause responsible for the decline of yellow cedars.
Second, although bears damage some trees, there’re not the cause of the overall population decline. Yellow cedar population’s been declining all across the northwestern coast of North America both on the mainland and on islands just off the coast. There were no bears on the islands, yet the islands cedars are still in decline. Since the decline occurs with and without bears, the bears cannot be responsible.
And finally, the theory about roots suffering from frost damage, well, the reading passage forgot to take one factor into account. Many more trees are dying at lower elevations where it is warm than at higher elevations where it is cold. If freezing damage were responsible for the decline, we could expect to see more trees dying in the cold weather of higher elevations. Instead, more trees are dying in the relative warmth of the lower elevations. So, although the climate change may have made the cedar roots more sensitive than it used to be, this isn’t what’s killing them.
一、阅读听力要点概括
Reading Passage
Main points: Scientist have some hypotheses to explain the drop of yellow cedar population.
Sub point 1: Decline caused by insect parasites.
Sub point 2: Decline caused by brown bears for food.
Sub point 3: Decline caused by cold winter.
.
Lecture
Attitude: Against. None explanations is adequate.
Sub Point 1: Healthy yellow cedars can resist insect infestation. (Poison. Tree already sick)
Sub Point 2: Bears are not the cause of overall decline. (Decline on no bear island)
Sub Point 3: Cold weather is not responsible for the decline. (Die at lower warm elevations)
Answer
二、范文逐段赏析
Paragraph 1
The lecturer holds that the main reason causing the overall decline in yellow cedar population has not yet been determined. The proposed reasons in the reading, though responsible for the poor health of some individual plants, may not account for the decline of the whole species throughout the North American Continent.
此段功能：
(Listening passage后文提到用L代替)
(Reading passage后文用R代替)
以L为根本，指出L反对R的结论，说造成黄杉树群总数下降的原因还未确定。随后复述R的观点，指出这些原因只能造成不健康的树木的死亡而不能造成北美总数量的下降。
此段结构：
首段第一句话以L出发，复述了L的结论，确认逻辑为相反。第二句复述R的结论，使读者明白了L和R要争论的点。随即准备讨论。
Paragraph 2
First, healthy yellow cedar trees can secrete a chemical that is poisonous to insects feeding on its bark. Hence, it is unlikely that the cedar bark beetle can ever attack one of these trees before it falls ill or dies. The reading thus finds a misleading causal relationship between the insect and the tree.
此段功能：
在第一个分论点中，L列举证据显示健康的黄杉能分泌出毒液防止虫害。所以其实这些虫子基本不可能导致健康树的死亡。随后指出并不像R说的那样，其实树的死亡和虫害没什么关系。
此段结构：
此段为分总结构。为了证明R的逻辑的不严密性，先列举了L中的真实证据，得出L的结论，最后说明R的结论是误导。
Paragraph 3
Second, bears cannot be blamed for the large-scaled death of yellow cedars across North America, although they might be responsible for the accidental death of some individual trees. Another condition that can absolve bears of this accusation is that yellow cedars growing on bear-free islands are also dying in large numbers. Hereby the reading material fails to identify the primary reason again.
此段功能：
在第二个分论点中，作者还是做总结，列举了L的证据和观点，熊是不能造成大规模黄杉死亡的，最多也就只能造成个别死亡，因为没有熊存在的岛屿，黄杉也在大量死亡。这样看来，R的结论自然不对。
此段结构：
此段为总分总结构，先总结L的结论的正确性并列举证据，最后一句又总结了R是不正确的。
Paragraph 4
Third, cold climates also cannot be blamed for the general decline in cedar population. The proof can be found in the trees’ wider recession in areas of lower elevation, where the temperature is warmer than at higher elevations. Though cold weather may have made cedars more sensitive, it is not the primary killer as the reading indicates.
此段功能：
讨论最后一个原因，总结冷天气是不能造成大面积黄杉下降的。原因是，在低纬度温暖地区，黄杉在大量死亡，在高纬度寒冷地区并没有出现比温暖区死亡更多的情况。虽然冷天气造成了黄杉的更敏感，但不是元凶。
此段结构：
此段为总分结构，第一句复述L的结论。并很好了做了类比，证明L的正确性。
三、范文全篇总评
1、 逻辑结构
全文遵从总分结构，第一段立刻指出L觉得造成黄杉数量下降的原因 not yet been determined，所以对R的态度主要是，R的解释都不充分(not adequate).
在接下来3段的分论点中，L分别对R的结论中的证据进行了更新，说明R之前做出的粗略的结论是不充分的。真实的原因还有待考察。
2、语言表达
本文语言表达，没有用复杂的句式，也没有大量采用难词生词，论证却十分准确。分段开头用1st,2nd,3rd虽然老套，但是叙述十分清楚。其中一些列举证据，论点可以借鉴的句式：
1. …..(论点A)……。The proof can be found…..(证据A).
The defendant is not guilty. The proof can be found when new evidence is processed.
2. absolve (某物，某人，某事件) of this accusation
免除(某)的责任。
The newly found evidence can absolve the defendant of his accusation of murder.