The sloth bear, an insect-eating
animal native to Nepal, exhibits only one
behavior that is truly distinct from that of
Line other bear species: the females carry
(5) their cubs (at least part-time) until the
cubs are about nine months old, even
though the cubs can walk on their own
at six months. Cub-carrying also occurs
among some other myrmecophagous
(10) (ant-eating) mammals; therefore, one
explanation is that cub-carrying is
necessitated by myrmecophagy, since
myrmecophagy entails a low metabolic
rate and high energy expenditure in
(15) walking between food patches. How-
ever, although polar bears’ locomotion
is similarly inefficient, polar bear cubs
walk along with their mother. Further-
more, the daily movements of sloth
(20) bears and American black bears—
which are similar in size to sloth bears
and have similar-sized home ranges—
reveal similar travel rates and distances,
suggesting that if black bear cubs are
(25) able to keep up with their mother, so
too should sloth bear cubs.
An alternative explanation is defense
from predation. Black bear cubs use
trees for defense, whereas brown bears
(30) and polar bears, which regularly inhabit
treeless environments, rely on aggres-
sion to protect their cubs. Like brown
bears and polar bears (and unlike other
myrmecophagous mammals, which are
(35) noted for their passivity), sloth bears
are easily provoked to aggression.
Sloth bears also have relatively large
canine teeth, which appear to be more
functional for fighting than for foraging.
(40) Like brown bears and polar bears,
sloth bears may have evolved in an
environment with few trees. They are
especially attracted to food-rich
grasslands; although few grasslands
(45) persist today on the Indian subcontinent,
this type of habitat was once wide-
spread there. Grasslands support
high densities of tigers, which fight and
sometimes kill sloth bears; sloth bears
(50) also coexist with and have been killed
by tree-climbing leopards, and are often
confronted and chased by rhinoceroses
and elephants, which can topple trees.
Collectively these factors probably
(55) selected against tree-climbing as a
defensive strategy for sloth bear cubs.
Because sloth bears are smaller than
brown and polar bears and are under
greater threat from dangerous animals,
(60) they may have adopted the extra pre-
caution of carrying their cubs. Although
cub-carrying may also be adoptive for
myrmecophagous foraging, the behavior
of sloth bear cubs, which climb on their
(65) mother’s back at the first sign of danger,
suggests that predation was a key
stimulus.
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Q9:
The primary purpose of the passage is to
trace the development of a particular behavioral characteristic of the sloth bear
explore possible explanations for a particular behavioral characteristic of the sloth bear
compare the defensive strategies of sloth bear cubs to the defensive strategies of cubs of other bear species
describe how certain behavioral characteristics of the sloth bear differ from those of other myrmecophagous mammals
provide an alternative to a generally accepted explanation of a particular behavioral characteristic of myrmecophagous mammalsD
答案呢是B，我怎么看怎么是E，由第二段首“An alternative explanation is defense from predation”， 很显然是两端式文章，第一断提出错误观点，第二段给出一个alternative的正确观点。应该是ETS的preference呀。  | 
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发表于 2004-12-9 18:01:00
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