阅读理解 Determining whether a given population of animals constitutes a distinct species can be difficult because no single accepted definition of the term exists. One approach, called the biological species concept, bases the definition on reproductive compatibility. According to this view, a species is a group of animals that can mate with one another to produce fertile offspring but cannot mate successfully with members of a different group. Yet this idea can be too restrictive. First, mating between groups labeled as different species (hybridization), as often occurs in the canine family, is quite common in nature. Second, sometimes the differences between two populations might not prevent them from interbreeding, even though they are dissimilar in traits unrelated to reproduction; some biologists question whether such disparate groups should be considered a single species. A third problem with the biological species concept is that investigators cannot always determine whether two groups that live in different places are capable of interbreeding.
When the biological species concept is difficult to apply, some investigators use phenotype, an organism's observable characteristics, instead. Two groups that have evolved separately are likely to display measurable differences in many of their traits, such as skull size or width of teeth. If the distribution of measurements from one group does not overlap with those of another, the two groups might reasonably be considered distinct species.

单选题 1.The passage is primarily concerned with

A、 describing the development of the biologica species concept
B、 responding to a critique of reproductive compatibility as a criterion for defining a species
C、 considering two different approaches to identifying biological species
D、 pointing out the advantage of one method of distinguishing related species
E、 identifying an obstacle to the classification of biological species

【正确答案】 C

【答案解析】Main idea
This question depends on understanding the passage as a whole. The passage begins by explaining that identifying a species can be difficult, because there are different ways of defining the term. The biological species concept is one approach, but it has problems. Phenotype is another approach that can be used when the biological species concept proves difficult.
A The first paragraph defines the biological species concept and identifies some problems with its application, but it does not explain how that concept developed.
B The passage presents some critiques of reproductive compatibility as a way of identifying a biological species; it does not concern itself with responding to those critiques.
C Correct. The passage considers the biological species concept and the idea of phenotype as ways of identifying biological species.
D While the passage identifies two ways of distinguishing species and states that some investigators use one of those methods- -the phenotype method—when the biological method is difficult to apply, the passage is not primarily concerned with pointing out that either one is better than the other.
E The passage does discuss certain obstacles to the classification of species. First, it points out that there is no single accepted definition of distinct species. Second, it points out obstacles related to one particular approach to the classificatior of species. However, the passage consider: these obstacles in service of its primary concern, namely considering two different approaches to identifying biological species.
The correct answer is C.

单选题 2.The author of the passage mentions "groups that ive in different places" (line 21) most probably in ordef to

A、 point out a theoretical inconsistency in the biological species concept
B、 offer evidence in support of the biological species concept
C、 identify an obstacle to the application of the biological species concept
D、 note an instance in which phenotype classification is customarily used
E、 describe an alternative to the biological species concept

【正确答案】 C

【答案解析】Evaluation
The author's mention of groups that live in different places comes at the end of the first paragraph, in the context of discussing a third problem with the biological species concept: that investigators may not know whether animals in such groups are able to interbreed.
A The author does not address theoretical inconsistencies in the biological species concept.
B The author mentions groups that live in different places in order to address a problem with the biological species concept, not to support it.
C Correct. One obstacle to applying the biological species concept is that those attempting to distinguish among species may not be able to determine whether geographically separated groups of animals can interbreed.
D The passage does mention that some investigators use phenotype classification when the biological species concept is difficult to apply, but it does not mention specifically that a situation in which groups live in different places is an instance in which phenotype classification is customarily used.
E Animal groups that live in different places pose a problem for the application of the biological species concept, according to the author. The author does not mention these groups in order to describe an alternative to that concept.
The correct answer is C.

单选题 3.With which of the following statements regarding the classification of individual species would the author most likely agree?

A、 Phenotype comparison may help to classify species when application of the biological species concept proves inconclusive.
B、 Because no standard definition exists for what constitutes a species, the classification of animal populations is inevitably an arbitrary process.
C、 The criteria used by biologists to classify species have not been based on adequate research.
D、 The existence of hybrids in wild animal species is the chief factor casting doubt on the usefulness of research into reproductive compatibility as a way of classifying species.
E、 Phenotype overlap should be used as the basic criterion for standardizing species classification.

【正确答案】 A

【答案解析】Inference
This question depends on understanding the general points the author makes with regard to classification of individual species. The author explains that there is no single definition of species and then describes the biological species concept, which depends on reproductive compatibility. This approach has several problems, however, and the author goes on to say that phenotype may be used when the biological species concept is difficult to apply.
A Correct. The author states at the beginning of the second paragraph that some investigators use phenotype when they find it difficult to apply the biological species concept, and the passage provides no reason to believe that the author would disagree with the idea that phenotype comparison can be helpful in these situations.
B The author would most likely not agree that classification of animal populations is arbitrary. Investigators use clearly defined approaches, such as the biological species concept and phenotype classification, to make such classifications. That there may be problems with an approach does not make it arbitrary.
C The author states that the biological species concept can be too restrictive, but there is no suggestion that the author finds this approach, or phenotype classification, to be inadequately researched.
D The author mentions hybridization first as a factor casting doubt on the usefulness of the biological species concept, but nothing in the passage suggests that the author thinks that it is more significant than the other reasons offered for finding the biological species concept too restrictive.
E Phenotype overlap does not receive the author's endorsement as the best, or most basic, way of classifying species; instead, the author states merely that some investigators rely on this approach when they cannot apply the biological species concept.
The correct answer is A.

单选题 4.Which of the following best describes the function of lines 10-13?

A、 It elaborates the definition of the biological species concept given in a previous sentence.
B、 It develops a point about the biological species concept made in the previous sentence.
C、 It states the author's central point about the biological species concept.
D、 It identifies a central assumption underlying the biological species concept.
E、 It demonstrates why the biological species concept is invalid.

【正确答案】 B

【答案解析】Evaluation
The sentence in question discusses hybridization as a first factor complicating the applicability of the biological species concept. Thus its function is to help explain why, as the previous sentence states, that concept is too restrictive.
A The sentence in question brings up a problem with the biological species concept; it does not elaborate the definition of that concept.
B Correct. According to the sentence that precedes the sentence in question, the biological species concept can be too restrictive. The author offers three reasons to develop this point, and the first reason is given in the sentence in question.
C The sentence in question could be said to support the author's central point about the biological species concept—that it is one (flawed) way of determining whether a population is a species—but it does not state that central point.
D The sentence in question expresses a problem with the biological species concept, not a central assumption of it.
E The sentence in question serves to indicate a problem with the biological species concept, but it does not go so far as to demonstrate that it is invalid.
The correct answer is B.