GWD24第一篇，没人问过

GWD-24 Q3 TO 6

More selective than most chemical

   pesticides in that they ordinarily destroy

only unwanted species, biocontrol.

Line agents (such as insects, fungi, and

(5) viruses) eat, infect, or parasitize tar-

   geted plant or animal pests. However,

   biocontrol agents can negatively affect

   nontarget species by, for example,

   competing with them for resources: a

(10) biocontrol agent might reduce the bene-

fits conferred by a desirable animal

species by consuming a plant on which

the animal prefers to lay its eggs.

Another example of indirect negative.

(15) consequcnces occurred in England

when a virus introduced to control

rabbits reduced the amount of open

ground (because large rabbit popu-

lations reduce the ground cover), in

(20) turn reducing underground ant nests

and triggering the extinction of a blue

butterfly that had depended on the

nests to shelter its offspring. The

paucity of known extinctions or disrup-

(25) tions resulting from indirect interactions

may reflect not the infrequency of such

mishaps but rather the failure to look

for or to detect them: most organisms

likely to be adversely affected by

(30) indirect interactions are of little or

no known commercial value and the

events linking a biocontrol agent with

an adverse effect are often unclear.

Moreover, determining the potential

(35) risks of biocontrol agents before they

are used is difficult, especially when a

nonnative agent is introduced, because,

unlike a chemical pesticide, a biocontrol

agent may adapt in unpredictable ways.

(40) so that it can feed on or otherwise harm

new hosts.

The example presented by the author in

lines 14-23 most clearly serves to illustrate

1. a situation in which a species is less

vulnerable to biocontrol agents than it

would have been to chemical pesticides.

2. a way in which the introduction of a bio-

control agent can affect a nontarget

species.

3. a nonnative agent’s adapting in an unpre-

dictable way that results in damage to a

new host.

4. The contention that biocontrol agents can

harm nontarget species by competing

with them for resources

5. the way in which indirect consequences

from the use of biocontrol agents are

most likely to occurs.

搜索不到，可能只有我不懂：（

答案是B，我想知道为什么D不对？两个例子不都是证明biocontrol agentscan harm nontarget species by competing with them for resources？

2. a way in which the introduction of a bio-control agent can affect a nontarget

species.

with them for resources

我也错了

应该是contention的问题,没有争论的