阅读材料：
The cane toad is a large (1.8 kg) amphibian species native to Central and South America. It was deliberately introduced to Australia in 1935 with the expectation that it would protect farmers’ crops by eating harmful insects. Unfortunately, the toad multiplied rapidly, and a large cane toad population now threatens small native animals that are not pest. Several measures have been proposed to stop the spread of the cane toad in Australia.
蔗蜍是一种原产于中南美洲的两栖动物，个头很大，重大1.8公斤。蔗蜍是在1935年由人工引进至澳大利亚的。因为它们可以吃害虫，所以希望借由它们保护农作物。不幸的是，蔗蜍繁殖迅速。而且，数量巨大的蔗蜍群体已经开始威胁一些对农业无害的小型本土生物。现在提出了几个解决蔗蜍在澳大利亚蔓延的方法。
One way to prevent the spread of the toad would be to build a national fence. A fence that blocks the advance of the toads will prevent them from moving into those parts of Australia that they have not yet colonized. This approach has been used before: a national fence was erected in the early part of the twentieth century to prevent the spread of rabbits, another animal species that was introduced in Australia from abroad and had a harmful impact on its native ecosystems.
第一个阻止蔗蜍蔓延的方法是建立一个全国范围的围栏。用围栏控制蔗蜍增长的方式是通过阻止它们迁徙实现的，这样它们就不会聚集到那些尚未被它们控制的地区了。这种方法以前就用过。在二十世界初期，澳大利亚就从用这种围栏阻止兔子的过度增长。兔子由澳大利亚从他国引进后，给当地的生态平衡造成了巨大的灾难。
Second, the toads could be captured and destroyed by volunteers. Cane toads can easily be caught in simple traps and can even be captured by hand. Young toads and cane toad eggs are even easier to gather and destroy, since they are restricted to the water. If the Australian government were to organize a campaign among Australian citizens to join forces to destroy the toads, the collective effort might stop the toad from spreading.
第二，可以招募志愿者抓蔗蜍。简单的陷阱就可以抓到蔗蜍，甚至徒手都可以抓到。至于蝌蚪和卵因为是生活在水里的，更是容易抓到和消灭。如果澳大利亚政府组织一个由澳大利亚公民参与的运动去消灭蔗蜍，那么可能会达到阻碍其蔓延的目的。
Third, researchers are developing a disease-causing virus to control the cane toad populations. This virus will be specially designed: although it will be able to infect a number of reptile and amphibian species, it will not harm most of the infected species; it will specifically harm only the cane toads. The virus will control the population of cane toads by preventing them from maturing and reproducing.
第三，研究人员正在研究一种用于控制蔗蜍数量的致病病毒。这种病毒是专门为控制蔗蜍研制的。尽管这种病毒也可以感染相当多数量的爬行动物和两栖动物，但是这种感染基本是无害的。它只会影响蔗蜍。这种病毒通过阻碍蔗蜍的蔗蜍的成熟和繁殖实现控制其数量的目的。
