国内题 92年02月 sectionA长阅读一道小题

songxiaoshiUID: 3170134

The more that is discovered about the intricate organization of the nervous system, the more it seems remarkable that genes can successfully specify the development of that system. Human genes contain too little information even to specify which hemisphere of the brain each of a human’s 1011 neurons should occupy, let alone the hundreds of connections that each neuron makes. For such reasons, we can assume that there must be an important random factor in neural development, and in particular, that errors must and do occur in the development of all normal brains.
The most vivid expression of such errors occurs in genetically identical (isogenic) organisms. Even when reared under the same conditions, isogenic organisms are rarely exact copies of one another, and their differences have revealed much about the random variations that result from (result from: v.由...产生) an organism’s limited supply of genetic information. In isogenic Daphniae, for example, even though the position, size, and branching pattern of each optic neuron are remarkably constant, there is some variability in connectivity, and the number of synapses varies greatly. This variability is probably the result of random scatter beyond the resolution of genetic control and is best termed “imprecision,” since its converse, the degree of clustering about a mean, is conventionally, called “precision.”
Imprecision should be distinguished from developmental mistakes: wrongly migrated neurons, incorrect connections, and the like. To use a computer analogy, minor rounding-off errors occur universally and are analogous to imprecision, but occasionally a binary digit is incorrectly transmitted, perhaps ruining a calculation, and this incorrect transmission is analogous to a developmental mistake. Thus, imprecision is a form of inaccuracy inherent within the limits of design, but mistakes are forms of gross fallibility.
Both imprecision and gross fallibility can plausibly be blamed on the insufficiency of genetic information, since either could be reduced by adding more information. It is universally accepted among information theorists that codes and languages can be made mistake-resistant by incorporating redundancy. However, since the amount of space available in any information system is limited, increased redundancy results in decreased precision. For example, π when written incorrectly in English, “three point oen four two, “can be understood correctly even though a typographical error has occurred. More precision could be gained, however, if those 24 spaces were filled with Arabic numerals (Arabic numerals: n.阿拉伯数字); then π could be expressed to 23 significant digits (one of the digits of a number beginning with the digit farthest to the left that is not zero and ending with the last digit farthest to the right that is not zero or is a zero considered to be exact called also significant figure), although any error would significantly change the meaning. There exists a trade-off (a giving up of one thing in return for another: EXCHANGE), the more precisely a system is specified, using a given limited amount of information, the greater the danger of gross mistakes. The overall scheme by which genetic information is rationed out (ration out: adv.应按配额给定地) in organisms, therefore, must involve a compromise between two conflicting priorities: precision and the avoidance of gross mistakes.

22.
The author uses all of the following to clarify the distinction between imprecision and gross mistake in neural development EXCEPT
(A) classification of borderline(borderline adj.边界的;模糊地带) phenomena
(B) a description of the relationship between the phenomena denoted by each term
(C) specific examples of the phenomena denoted by each term
(D) an explanation of at least one of the key terms involved（A）
(E) analogies to other types of phenomena
这题百思不得其解,phenomena指的是什么呢???我都没有找到imprecision和gross mistake的phenomenon.
有没有同学做过这个题麻烦告诉我一下?O(∩_∩)O谢谢

songxiaoshiUID: 3170134

顶一下!