【正确答案】The examples provided fall into the category of slang, which is a causal use of language that consists of expressive but nonstandard vocabulary, typically of arbitrary, flashy and often ephemeral coinages and figures of speech characterized by spontaneity and sometimes by raciness the central characteristic of slang comes from the motive for its use: a desire for novelty, for vivid emphasis, from membership in a particular group or class of people whose "community argot" may be in comprehensible for outsider, or for being up with the times or a little ahead.
   As for some slang, we may identify their real meaning based on their literal meaning. However, more often than not, it is extremely difficult for us to figure out what it really means without related knowledge and culture background. I will classify the examples into two groups according to the degree of identificationality of the slang. The first group is the slang which we may identify its meaning; including "castles in the air, foot the bill, tighten one's belt, throw the book at, and turn the tables on" we can detect their meanings simply by interpreting the literal words and making some associations. Although we cannot figure out the precise meaning of these items, we would not be hampered during the process of comprehension. The second group embodies the rest items, "bum the candle at both ends, shoot the breeze, play it by ear, and pull one's leg" As for this group, the way for interpretation does not work here. If we tried to interpret them from the literal level, we may end up at a loss, having no idea what it really conveys. This is especially difficult for foreign learners who have no access to relevant knowledge or culture background.
   (本题主要考查社会语言学的小分支——俚语的应用。考生可以从不同角度来分类和论证。)