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以下是引用dorbear在2003-11-2 12:47:00的发言：
对，应该是。最好用一道题来讨论最能理解清楚。
好的，我以前问过两道题：
18. Advertisement: Attention pond owners! Ninety-eight percent of mosquito larvae in a pond die within minutes after the pond has been treated with BTI. Yet BTI is not toxic to fish, birds, animals, plants, or beneficial insects. So by using BTI regularly to destroy their larvae, you can greatly reduce populations of pesky mosquitoes that hatch in your pond, and you can do so without diminishing the populations of fish,
frogs, or beneficial insects in and around the pond.
Which one of the following is an assumption on which the argument depends?
(A) The most effective way to control the numbers of mosquitoes in a given area is to destroy the mosquito larvae in that area.
(B) Populations of mosquitoes are not dependent on a single body of water within an area as a place foe their larvae to hatch and develop
(C) There are no insect pests besides mosquitoes that pond owners might want to eliminate from in and around their pond.
(D) The effectiveness of BTI in destroying mosquito larvae In a pond does not require the pond owner’s strict adherence to specific application procedures.
(E) The fish, frogs, and beneficial insects in and around a pond-owner’s pond do not depend on mosquito larvae as an important source of food.
key:E 为什么A不对呢？
X: Since many chemicals useful for agriculture and medicine derive from rare or endangered plant species,it is likely that many plant species that are now extinct could have provide us with substances that would have been a boon to humanity. Therefore, if we want to ensure that chemicals from plants are available for
use in the future, we must make more serious efforts to preserve for all time our natural resource.
Y: But living things are not our “resources.” Yours is a selfish approach to conservation. We should rather strive to preserve living species because they deserve to survive, not because of the good they can do us.
8. X’s argument relies on which one of the following assumptions?
(A) Medicine would now be more advanced than it is if there had been a serious conservation policy in the past.
(B) All living things exist to serve humankind.
(C) The use of rare and endangered plant species as a source for chemicals will not itself render those species extinct.
(D) The only way to persuade people to preserve natural resources is to convince them that it is in their interest to do so.
(E) Few, if any, plant species have been saved from extinction through human efforts.
答案是C，为什么D不对？
第一题的so＝therefore ，其后用的是by的方式状语。
第二题的therefore，后面用的是if条件句。
如果按照CXD的思维方式，therefore后面由if条件句，可以推出后面主句的内容，那therefore前面的内容其实可以只看成是一个context，在作演绎题时，他们是否可以不用考虑，而只须对
by.......,you can......；if........,we must......这些结构进行分析就可以了？呵呵，傻傻的问题，请多指教！ | 
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发表于 2003-11-2 09:06:00
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