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按摩擦类型分类，导轨可以分为：滑动摩擦导轨，滚动摩擦导轨，弹性摩擦导轨，流体摩擦导轨等。其中（）导轨，低速时，容易产生爬行现象。
A . 滚动摩擦
B . 滑动摩擦
C . 弹性摩擦
D . 流体摩擦
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Slang , informal, nonstandard words and phrases , generally have shorter lives than the expressions of ordinary colloquial speech. The former are typically formed by creative , often witty juxtapositions of words or images. Slang can be contrasted with jargon (technical language of occupational or other groups) and with argot or cant (secret vocabulary of underworld groups) , but the borderlines separating these categories from slang are extremely blurred , and some writers use the terms cant , argot , and jargon in a general way to include all the foregoing meanings.Slang trends originate in subcultures within a society. Occupational groups (for example , loggers , police , medical professionals , and computer specialists) are prominent originators of both jargon and slang. Other groups creating slang include the armed forces , teenagers , racial minorities , ghetto residents , labor unions , citizen-band radiobroadcasters , sports groups , drug addicts , criminals , and even religious denominations (Episcopalians , for example , produced the term ‘spike' , meaning a High Church Anglican). Slang expressionsoften embody attitudes and values of group members. They may thus contribute to a sense of group identity and may convey to the, listener information about the speaker' s background. Before an apt expression becomes slang , however , it must be widely adopted by members of the subculture. At this point slang and jargon overlap greatly. If the subculture has enoughcontact with the mainstream culture , its figures of speech become slang expressions known to the whole of society. For example , cool cat (aloof , stylish person) , Mr. Charley (a white man) , The Man (the law) , and Uncle Tom (a meek black) all originated in the predominantly black Harlem district of New York City and have traveled far since their inception. Slang is thus generally not tied to any geographic region within a country.A slang expression may suddenly become widely used and as quickly dated (skiddoo). It may become accepted as standard speech , either in its original slang meaning (bus , from omnibus) or with an altered , possibly tamed meaning (jazz , which originally had sexual connotations). Some expressions have persisted for centuries as slang (booze for alcoholic beverage). In the 20th century , mass media and rapid travel have sped up both the circulation and the demise of slang terms. Television and novels have turned criminal cant into slang (five grand for $5000). Changing social circumstances may stimulate the spread of slang. Drug-related expressions (such as pot and marijuana) were virtually a secret jargon in the 1940s; in the 1960s they were adopted by rebe11ious youth; and in the 1970s and '80s they were widely known.26. The passage mainly discusses ( )·A. the social function of slang and jargonB. the origins of slang and its social applicationC. how jargon differs from slangD. the relationship between slang and subcultures27. With reference to the outstanding contributors to the birth of slang , the author mentions all of the followingexcept ( )A. athletesB. clergyC. doctorsD. philosophers28. The word They in para. 2 refers to ( )A. slang expressionsB. group membersC. attitudes and valuesD. the speakers29. Slang expressions contribute toA. the identification of individuals speech patternsB. the basic lifestyle. of a certain groupC. the identity of people as individualsD. the identification of a social group30. Which of the following , according to the passage , contributed to accelerating the metabolism (新陈代谢) of slang expressions in the 20th century ?A. Newspapers and magazinesB. Rebellious youthC. Religious denominationsD. Drug--users
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