Over the last 40 years there has been a great increase not only in the number
* |" N$ E4 R2 W7 Wof agricultural pesticides in use but also in the care and sophistication with which
4 A. O; x) t% P2 z( uthey are used by farmers. Nevertheless, the proportion of agricultural crops lost ( s, Y# Q- r: ~
to certain pests worldwide has increased over the same period, even when the : v# j/ A7 \: T) N
pests concerned have not developed resistance to existing pesticides.
# V/ E |/ ]3 d1 ` Which of the following, if true, best explains how improvements in pesticide use 6 w% }8 ?. d6 [$ D+ D/ J; ^, i
have been accompanied by greater losses to certain pests?
7 K7 V$ g) r5 D4 W, J& L. w, K0 @ A Some dangerous but relatively ineffective pesticides common 40 years ago ) B1 n5 t! E9 K( }" x: d
are no longer in widespread use.
/ h1 v6 V/ a4 p6 T B As pesticides have become increasingly pest-specific, controlling certain ) i) I# _, h0 f4 a- V" i
pests with pesticides has turned out to cost more in many cases than the $ j4 R& I7 P8 _
value of crop losses caused by those pests. 3 g2 v8 e5 t9 A
C Because today's pesticides typically have more specific application condi-
" V/ F4 y& `1 d, V6 a tions than did pesticides in use 40 years ago, today's farmers observe
( N* C2 H8 C/ | their fields more closely than did farmers 40 years ago.
# C: i/ ~" n: u p! Y* H D Certain pest-control methods that some farmers use today do not involve
/ k( i& x5 _; |0 Y the use of chemical pesticides but are just as effective in eliminating insect 8 O! K' ?, d, f3 Y5 R
pests as those that do.
3 N7 }0 y/ E0 T/ a) r) ~" ~ E Forty years ago, much less was known about the effects of pesticides on * J4 r+ I- l5 x* O
humans and other mammalian species than is now known.
6 c) @' T% ~2 H* O: l, u答案 B |
发表于 2012-8-15 12:40:43
