Over the last 40  years there has been a great increase not only in the number

of agricultural pesticides in use but also in the care and sophistication with which

they are used by farmers.  Nevertheless, the proportion of agricultural crops lost

to certain pests worldwide has increased over the same period, even when the

pests concerned have not developed resistance to existing pesticides. 

 Which of the following, if true, best explains how improvements in pesticide use

have been accompanied by greater losses to certain pests?

     A   Some dangerous but relatively ineffective pesticides common 40 years ago

       are no longer in widespread use. 

    B   As pesticides have become increasingly pest-specific, controlling certain

       pests with pesticides has turned out to cost more in many cases than the

       value of crop losses caused by those pests. 

     C  Because today’s pesticides typically have more specific application condi-

       tions than did pesticides in use  40  years ago, today’s farmers observe

       their fields more closely than did farmers 40  years ago. 

    D  Certain pest-control methods that some farmers use today do not involve

       the use of chemical pesticides but are just as effective in eliminating insect

       pests as those that do. 

    E  Forty years ago, much less was known about the effects of pesticides on

       humans and other mammalian species than is now known. 

答案 B