Reading Comprehension

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 targeted
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 benefits
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 populations
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.

6
The example presented by the author in
lines 14-23 most clearly serves to illustrate
A. a situation in which a species is less
vulnerable to biocontrol agents than it
would have been to chemical pesticides.
B. a way in which the introduction of a biocontrol
agent can affect a nontarget
species.
C. a nonnative agent's adapting in an unpredictable
way that results in damage to a
new host.
D. The contention that biocontrol agents can
harm nontarget species by competing
with them for resources
E. the way in which indirect consequences
from the use of biocontrol agents are
most likely to occurs.

OA is B . Why not E.