請依下文回答第 46 題至第 50 題：    In the United States, there are about twenty-two million hearing-impaired people; of these, two million areprofoundly deaf (unable to hear any thing) or severely deaf (unable to hear much). Hearing impairment resultsfrom three major factors that are not necessarily exclusive: environmental, hereditary and old age.    Environmental causes include noise-induced, accidental, toxic, and viral. Noise-induced deafness is primarilya phenomenon of the modern industrial world, though stonemasons, may have been subject to hearing-loss in theancient world. Permanent deafness resulting from toxicity is also a phenomenon of the modern world. Deafnessfrom accident, such as a blow to the ear, must have resulted from time to time. Viruses, too, were very much partof the ancient world. Of the six main viruses that can cause deafness today—chickenpox, common cold viruses,influenza, measles, mumps, and poliomyelitis—there is evidence for five in ancient Greece. There is alsoevidence for the presence of bacterial meningitis, whose classic complication is hearing loss. In modern,developed countries, preventative medicine reduces the incidence and severity of these viruses, but in the ancientworld, as in third-world countries today, these viruses must have taken their toll.    There is no reason to rule out hereditary deafness in the ancient world, and there is some conjecturalevidence for the results of in-breeding, although not specifically for deafness. In addition to inbreeding, otherhereditary factors would have produced deafness. Some families simply have a genetic background that favorsdeafness.
46 Compared to the ancient world, what is the chief factor that causes the loss of hearing in the modernindustrial world?
(A) virus
(B) noise
(C) measles
(D) inbreeding