Loudspeakers were fixed to _____ everyone an opportunity to hear the speech.

Loudspeakers were fixed in the hall so that everyone _____ an opportunity to hear the speech.

What facilities are used for conference? A: projection screens B: loudspeakers C: floodlights D: projector

Several loudspeakers are _______ from the ceiling and we can hear the speaker very clearly.

Loudspeakers were fixed in the hall so that everyone_____ an opportunity to hear the speech. A: ought to have B: must have C: may have D: should have

Loudspeakers were fixed in the hall so that everyone______ an<br/>opportunity to hear the speech. A: ought to have B: must have C: may have D: should have

Modern technology may not haveimproved the world all that much but it certainly has made life noisier. Unruffledmotorcycles, blaring car alarms, and roving boom boxes come first, second, andthird on my list of most obnoxious noise offenders, but everyone could come upwith his own version of aural hell – if he could just find a quiet spot toponder the matter. Yet what technology has done, othertechnology is now starting to undo, using computer power, to zap thoseear-splitting noises into silence. Previously silence-seekers had littlerecourse except to stay inside, close the windows, and plug their ears.Remedies like these are quaintly termed “passive” systems, because they placephysical barriers against the unwanted sound. Now computer technology isproducing a far more effective “active” system, which doesn’t just contain,deflect, or mask the noise, but annihilates it electronically. The system works by countering theoffending noise with “anti-noise”, a somewhat sinister-sounding term that callsto mind antimatter, black holes, and other Popular Science mindbenders but thatactually refers to something quite simple. Just as a wave on a pond isflattened when it merges with a trough that is its exact opposite (or mirrorimage), so can a sound wave be negated by meeting its opposite. This general theory of soundcancellation has been around since the 1930s. In the fifties and sixties itmade for a kind of magic trick among laboratory acousticians playing aroundwith the first clunky mainframe computers. The advent of low-cost high-powermicroprocessors has made active noise-cancellation systems a commercialpossibility, and a handful of small electronics firms in the United States and abroad are bringing the first ones onto the silence market. Silence buffs might be hoping that the noise-canceling apparatus will takethe shape of the 44 Magnum wielded by Dirty Harry, but in fact active soundcontrol is not quite that active. The system might more properly be describedas reactive, in that it responds to sound waves already headed toward humanears. In the configuration that is usual for such systems microphones detectthe noise signal and send it to the system’s microprocessor, which almostinstantly models it and creates its inverse for loudspeakers to fire at theoriginal. Because the two sounds occupy the same range of frequencies andtones, the inverse sounds exactly like the noise it is to eliminate, theanti-noise canceling Beethoven’s Fifth Symphony is heard as Beethoven’s Fifth.The only difference is that every positive pressure produced on the air by theorchestra is matched by a negative pressure produced by the computer, and everynegative pressure is matched by a positive, thereby silencing the sound. The systemis most effective as a kind of muffler, in which microphones, micro-processor,and loudspeaker are all in a unit encasing the device that produces the sound,stifling it at its source. But it can work as a headset, too, negating thesound at the last moment before it disturbs one’s peace of mind. 1. The writer holds that( ). A. modern technology has disturbed thequiet life of the people B. moderntechnology has made people indifferent to noise pollution C. moderntechnology has made the present world quieter than before D.modern technology has failed to solve the problem of noise pollution 2. According to the passage,an active noise-cancellation system ( ). A. contains noise rather than negates it B. eliminates noise rather than muffles it C. deflects noise rather than baffles it D. holds noise back rather than stifles it 3. In paragraph 5 the word “buffs”means ( ). A. settlers B.enthusiasts C. buyers D. manufacturers 4. Which of the followingstatements is NOT true according to the passage? ( ) A.In the past, people sometimes plugged their ears to fight against the offendingnoise. B. An active noise-cancellation systemfollows the principle of a wave being flattened by meeting its exact opposite. C. The first active noise-cancellationsystem was made in the 1930s. D. Active noise-cancellation systems are nowavailable on the market. 5. Activenoise-cancellation systems require ( ). A. microphones B.microprocessors C.loudspeakers D. all of theabove

比较C≡C, C=C, C─C, C=C─C=C的键长次序为: C=C─C=C>C─C> C≡C >C=C|C=C─C=C>C─C>C=C>C≡C|C≡C>C=C>C─C>C=C─C=C|C─C>C=C>C=C─C=C>C≡C|C─C>C=C─C=C>C=C>C≡C

下列哪种主链骨架原子排列最能代表两个肽键?() A: Cα—N—Cα—C—Cα—N—Cα—C B: Cα—N—C—C—N—Cα C: C—N—Cα—Cα—C—N D: Cα—C—N—Cα—C—N E: Cα—Cα—C—N—Cα—Cα—C

比较C≡C(Ⅰ),C=C(Ⅱ),C─C(Ⅲ),C=C─C=C(Ⅳ)的键长次序为( )。 A: Ⅰ＞Ⅱ＞Ⅲ＞Ⅳ B: Ⅲ＞Ⅱ＞Ⅳ＞Ⅰ C: Ⅲ＞Ⅳ＞Ⅱ＞Ⅰ D: Ⅳ＞Ⅲ＞Ⅱ＞Ⅰ