单选题 What makes for a successful invasion? Often, the answer is to have better weapons than the enemy. And, as it is with people, so it is with plants—at least, that is the conclusion of a paper published in Biology Letters by Naomi Cappuccino, of Carleton University, and Thor Arnason, of the University of Ottawa, both in Canada.
The phenomenon of alien species popping up unexpected parts of the world has grown over the past few decades as people and goods become more mobile and plant seeds and animal larvae have hitched along for the ride. Most such aliens blend into the ecosystem in which they arrive without too much fuss. (Indeed, many probably fail to establish themselves at all—but those failures, of course, are never noticed.) Occasionally, though, something goes bananas and starts trying to take the place over, and an invasive species is born. Dr. Cappuccino and Dr. Arnason asked themselves why.
One hypothesis is that aliens leave their predators behind. Since the predators in their new homelands are not adapted to exploit them, they are able to reproduce unchecked. That is a nice idea, but it does not explain why only certain aliens become invasive. Dr. Cappuccino and Dr. Arnason suspected this might be because native predators are sometimes "pre-adapted" to the aliens' defences, but in other cases they are not.
To test this, they had first to establish a reliable list of invaders. That is not as easy as it sounds. As they observe, "although there are many lists of invasive species published by governmental agencies, inclusion of a given species in the lists may not be entirely free of political motivation". Instead, they polled established researchers in the field of alien species, asking each to list ten invasive species and, for comparison, ten aliens that just rubbed along quietly with their neighbours. The result was a list of 21 species widely agreed to be invasive and, for comparison, 18 non-invasive aliens.
Having established these lists, they went to the library to find out what was known about the plants' chemistry. Their aim was to find the most prominent chemical weapon in each plant, whether that weapon was directed against insects that might want to eat the plant, bacteria and fungi that might want to infect it, or other plants that might compete for space, water, nutrients and light. Botanists know a lot about which sorts of compounds have what roles, so classifying constituent chemicals in this way was not too hard.
The researchers then compared the chemical arsenals of their aliens with those of native North American plants, to see if superior (or, at least, unusual) weaponry was the explanation for the invaders' success. Their hypothesis was that highly invasive species would have chemical weapons not found in native plants, and which pests, parasites and other plants would therefore not have evolved any resistance to. The more benign aliens, by contrast, were predicted to have arsenals also found in at least some native species.
And so it proved. More than 40% of the invasive species had a chemical unknown to native plants, just over 10% of the non-invasive aliens had such a chemical. Moreover, when they looked at past studies on alien plants that had examined how much such plants suffer from the depredations of herbivorous insects, they found that the extent of the damage reported was significantly correlated with the number of native species with which that alien shared its principal chemical weapon.
For alien plants, then, the real secret of success—also as in human warfare—is surprise. It is not that the chemicals concerned are more toxic in any general sense (indeed, successful invaders are often rare in their own native habitats). Rather, it is that the locals just don't see them coming.

单选题 In dozens of years, there are more cases of the invasion of alien species partly because

单选题 The expression "something goes bananas" in Paragraph 2 probably means something

【正确答案】 C

【答案解析】语义理解题。由题干定位至第二段。第二句指出：这些外来物种大多数都轻而易举地融入了所到之处的生态系统。之后出现了occasionally一词，这与前文的most such aliens构成对比关系：不过，偶尔也有某些物种goes bananas，开始企图占领原有物种的生长空间，一种入侵物种就这样形成了。显然这里的goes bananas与上一句中的arrive without too much fuss是对比关系，too much fuss的意思是“太大惊小怪”，可以判断goes banana这个能够引起人们震惊的物种入侵一定是程度比较重，状态疯狂，这与后面的trying to take the place over构成衔接关系，故[C]符合语境。[A]是对字面肤浅解释，排除。[B]中的important是一个中性词，与take the place over无语义联系，排除。[D]中的frightening不符合语境，这里没有提到人们对外来物种是否感到害怕。

单选题 The difference between Dr. Cappuccino and Dr. Arnason's hypothesis and the previous one is that

【正确答案】 B

【答案解析】由题干中的hypothesis定位至第三段。前两句对其他人的假设进行了解释：有人推想，外来物种摆脱了原先的掠食者，而在新的“家园”，现有的掠食者又没有发现它们也合口味，因此这些物种得以肆无忌惮地繁衍。然后指出这一观点的问题：这种观点好是好，不过没有解释为什么只有特定的外来物种才具有人侵性。该段末句指出Dr Cappuccino和Dr Arnason的猜测：这可能是因为土生土长的掠食者对外来物种所具有的防御机制有时产生“预适应”，有时又不产生。显然，先前假设存在的问题就是这两个人研究的内容，故[B]为答案。从该段可知，两种假设都提及predators，排除[A]。提到pre-adapted的是Dr Cappuccino和Dr Arnason，[D]属于张冠李戴，排除。而[C]则为该先前假设的部分内容，但无法得知是否为两种假设的区别所在，排除。

单选题 The researchers didn't refer to the lists of invaders published by governmental agencies due to ______ consideration.

单选题 Which of the following is TRUE of chemical weapons of invasive species?

【正确答案】 B

【答案解析】细节题。由题干中的chemical weapons定位至第五段。第二句指出：他们就到图书馆查询这些植物的化学性质…，结合末句的“植物学家对哪些化合物有哪些作用都了如指掌，因此这样对化学物质进行分类并不太难”可判断[A]不符合文意。第六段第二句提到；他们推断，具有高度入侵性的物种拥有土产植物所缺少的“化学武器”，对这种化学武器，害虫、寄生虫及其他植物都不能产生任何抵抗力。[D]中的aliens和 highly invasive species概念不同，无法得出该项结论，排除。末句指出：入侵性较弱的外来物种所具有的“武器库”可能至少同样存在于某些土产物种。这里指的不是chemical weapons的数量多少，而是本地物种和外来物种是否有同样的武器库影响入侵性，排除[C]。从第六段首句“然后，为了弄清外来物种的成功入侵是否得益于超级武器，这两位研究人员将已知外来物种的化学武器库同北美土生土长的植物化学武器库进行了比较。”和第七段首句“猜测因而得到了证实。”可知[B]符合文意，故为答案。