Stop. Listen! What do you hear? You may hear many different sounds. Some of those sounds may be noise. Noise is a loud or unwanted sound. Noise can be caused by many kinds of machines, such as motorcycles, jet planes and farm tractors . Rock music is also noise. What happens to people who live near noisy machines or use them over a period of time? Doctors have found that these people have trouble in sleeping. But, most important, constant loud noise can cause a loss of hearing. Scientists use a unit of measure called decibel to measure the loudness of a sound. The sound of a quiet room, for example, measures 35 decibels. Talking measures between 40 and 65 decibels. Sounds from traffic and from some rock bands can measure over 120 decibels. Noise at this high level causes the great hearing loss. A decibel is a _ . A) unit that measures sound B) kind of noise C) machine that makes loud noise D) person who hates sound
A:
A