球思路

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?

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

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

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

D.   
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.

E.    
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.

在A,D 之间犹豫，答案是D 不知道A 为什么不可以？

请教思路