Our sense of hearing is one of the most important means of knowing what is going on around us. We are warned of er by sounds. The sounds of music please us. Sound has a waste product, too, in the form of noise. Noise has been called unwanted sound. Noise is growing and it may get much worse before it gets any better. Scientists, for several years, have been studying how noise affects people and animals and are alarmed by what they have learned. Peace and quiet are becoming harder to find. Noise pollution is no joke. It is a threat that should be looked at carefully. Sound is measured in units called decibels （分贝）. At a level of 140 decibels people feel pain in their ears. Trucks, buses, motorcycles, airplanes, boats, and factories all make noise. This noise bothers not only our ears, but our minds and bodies as well. There is a saying about 'it is so noisy that you can't hear yourself think'. Doctors who study noise believe that we must be able to hear ourselves think most of the time. If we don't, we may have headaches, other aches and pains, or even mental problems. Noise adds even more tension to a society which already faces too much stress. 49．The sense of hearing _______. A．makes people feel angry B．makes people want to dance C．helps people to know what is happening around them D．is something harmful to people 50．When sound is turned into noise, _______. A．people become ill                  B．it makes people forget the past C．people don't know how to deal with it  D．it becomes a kind of pollution 51．Why does the passage say ' Peace and quiet are becoming harder to find ' ? A．Sounds of over 140 decibels are common these days. B．There are always wars going on in the world. C．The world is more and more noise. D．All kinds of machines make noises. 52．Which of the following statements is TRUE? A．Scientists are warning people noise can be harmful. B．It's possible for man to get rid of all noises. C．Sounds under 140 decibels are not considered to be noise. D．Society has become more lively because there is noise now.