29. Biologists with a predilection for theory have tried—and largely failed—to define what it is that makes something a living thing. Organisms take in energy-providing materials and excrete waste products, but so do automobiles. Living things replicate and take part in evolution, but so do some computer programs. We must be open to the possibility that there are living things on other planets. Therefore, we will not be successful in defining what it is that makes something a living thing merely by examining living things on Earth—the only ones we know. Trying to do so is analogous to trying to specify ______.
Which of the following most logically completes the passage?

A、 the laws of physics by using pure mathematics
B、 what a fish is by listing its chemical components
C、 what an animal is by examining a plant
D、 what a machine is by examining a sketch of it
E、 what a mammal is by examining a zebra

【正确答案】 E

【答案解析】 Argument Construction
Situation Some biologists have tried, unsuccessfully, to find a theoretically defensible account of what it
means for something to be a riving thing. Some of the suggested definitions are too broad, because
they include things that we would not regard as riving. To find life on other planets, we must not
narrow our conception of life by basing it simply on the kinds of life encountered on Earth.
Reasoning Which of the five choices would be the logically most appropriate completion of the argument? The
argument points out that life-forms elsewhere in the universe may be very different from any of
the life-forms on Earth. Both life-forms on Earth and life-forms discovered elsewhere would all
qualify as members of a very large class, the class of all rife-forms. Taking rife-forms on Earth,
a mere subset of the class of all life-forms, as representative of all life-forms would be a logical
mistake and would not lead to success in defining what it means for something to be a living
thing.
A This would not involve a logical mistake like the one already identified.
B This would not involve a logical mistake closely resembling the one already identified.
C Plants are not a subclass of the class of animals, so this does not involve the logical mistake of taking a subclass as representative of a larger class.
D This does not involve a logical mistake closely resembling the one already discussed.
E Correct. This involves the logical mistake of taking the class of zebras, a subclass of the class of mammals, as representative of the class of mammals. Logically, it resembles taking the class of life-forms on Earth as representative of the class of all life-forms.
The correct answer is E.