ＧＷＤ１－３３　请指点一下

A company plans to develop a prototype weeding machine that uses cutting blades with optical sensors and microprocessors that distinguish weeds from crop plants by differences in shade of color.  The inventor of the machine claims that it will reduce labor costs by virtually eliminating the need for manual weeding.

Which of the following is a consideration in favor of the company’s implementing its plan to develop the prototype?

1. There is a considerable degree of variation in shade of color between weeds of different species.

2. The shade of color of some plants tends to change appreciably over the course of their growing season.

3. When crops are weeded manually, overall size and leaf shape are taken into account in distinguishing crop plants from weeds.

4. Selection and genetic manipulation allow plants of virtually any species to be economically bred to have a distinctive shade of color without altering their other characteristics.

5. Farm laborers who are responsible for the manual weeding of crops carry out other agricultural duties at times in the growing season when extensive weeding is not necessary.

没怎么读懂题，请ＮＮ指点一下，题目和选项啥意思啊，为什么选（Ｄ）我做的时候选Ｅ了，新手，请多关照，谢谢

题目是说：一个公司打算开发一种割草机，通过在刀具上安装光学识别设备和微处理器，割草机可以根据杂草和作物阴影颜色的不同来区分杂草和作物。发明者声称，通过这个设备，除草的人工成本可以大大降低

问题是说：是什么原因导致这个公司支持这个设备的开发

D的意思是：仅从暗处的颜色上就能够区分不同的物种，且选择和操作的过程是经济可行的。

E的意思是：除草员在不需要除草的季节可以干其他的工作。

显然，E无法说明公司的决策。A牵涉了设备工作原理，但不如D具体，主要是没有说到经济性；B说的是Crop本身在不同季节的Shade Color 变化，和这个设备的目的没有关系；C说的是一个不同的原理。

选项D是一个3级难句。

Selection and genetic manipulation {allow plants [of virtually any species] to be economically bred} to have a distinctive shade of color without altering their other characteristics.

To have 后面是一个倒装，用来说明Selection and genetic manipulation的前提；主句是 ~ allow plants to be bred (意思是“使得植物能够被区别品种”)。economically用来修饰bred，这个词体现了题目的最后一句，所以比答案选项A来得合适。

我刚开始复习，请大牛拍砖！