2016年12月英语四级考前冲刺试题第五套_第3页

　　You do not remain at this deep fourth stage all night long, but instead about 80 minutes after you fall into slumber, your brain activity level will increase again slightly. The delta rhythm will disappear, to be replaced by the activity pattern of brain waves. Your eyes will begin to dart around under your closed eyelids (眼皮) as if you were looking at something occurring in front of you. This period of rapid eye movement lasts for some 8 to 15 minutes and is called REM sleep. It is during REM sleep period, your body will soon relax again, your breathing will grow slow and regular once more, and you will slip gently back from stage 1 to stage 4 sleep only to rise once again to the surface of near consciousness some 80 minutes later.

　　26.The stages of sleep take on ____.

　　A) an irregular aspect. B) a regular aspect C) a punctual aspect D) a similar aspect

　　27.Stage 4 sleep lasts ____.

　　A) about 80 minutes

　　B) about 4060 minutes

　　C) about 30 munutes

　　D) about 2040 minutes

　　28.The brain waves are the slowest during ____.

　　A) stage 1 B) stage 2 and stage 3 C) stage 4 D) REM sleep

　　29.In the second paragraph the word “dart” means ____.

　　A) glare B) move rapidly or suddenly C) stop movingD) gaze

　　30.One of the features of REM sleep is that ____.

　　A) there are large slow waves, though rapid for the first few minutes

　　B) you have the deepest sleep

　　C) there are no brain waves

　　D) the brain waves are a little fast and the brain becomes a little active

　　Questions 31 to 35 are based on the following passage:

　　Designing a lens can be compared to playing chess. In chess a player tries to trap his opponent's king in a series of moves. In creating a lens a lens designer attempts to “trap” light by forcing all the rays arising from a single point in the subject to focus on a single point in the image, as a consequence of their passing through a series of transparent( 透明的) elements with precisely curved surfaces. Since in both cases the ultimate goal and the means by which it can be attained are known, one is tempted to think there will be a single best decision at any point along the way. The number of possible consequences flowing from any one decision is so large, however, as to bevirtually, if not actually, infinite. Therefore in lens design, as inchess, perfect solutions to a problem are beyond reach. Although this article will be concerned only with the design of photographic lenses, the same principles apply to all lenses.

　　The lens designer has one enormous advantage over the chess player: the designer is free to call on any available source of help to guide him through the staggering number of possibilities. Most of that help once came from mathematics and physics, but recently computer technology, information theory,chemistry, industrial engineering and psychophysics have all contributed to making the lens designer's job immeasurably more productive. Some of the lenses on the market today were inconceivable a decade ago. Others whose design is as much as a century old can now be massproduced at low cost. With the development of automatic production methods, lenses are made by the millions, both out of glass and out of plastics. Today's lenses are better than the best lenses used by the great photographers of the past.Moreover, their price may lower, in spite of the fact that 19thcentury craftsmen worked for only a few dollars a week and today's lenses are more complex. The lens designer cannot fail to be grateful for the science and technology that have made his work easier and his creations more widely available, but he is also humbled: it is no longer practical for a fine photographic lens to be designed from beginning to end by a single human mind.