Our sense of hearing is one of the most important means of knowing what is going on around us. We are warned of danger 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  . 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. When sound is turned into noise,   _  .
people become ill it makes people forget the past people don't know how to deal with it it becomes a kind of pollution
Question: Our sense of hearing is one of the most important means of knowing what is going on around us. We are warned of danger 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  . 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. 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
Answer: