D A team of scientists proved that seals had a very good sense of hearing. These men trained blind seals to expect food when they heard sounds. The seals always began snapping(猛咬) when a strong signal was sounded. It was proved that even a soft signal, a considerable distance away, could make these sea animals respond. That should make the fisherman who makes much noise while working, or talks loudly, start thinking. The same team of scientists also trained seals to recognize different sounds. One bell-tone meant food ,two bell-tones meant no food. In the beginning, the seals made mistakes when the two bell-tones were sounded. They were given a light tap after each mistake. The seals were good learners. They easily learned to tell the difference between the sounds. 67.Why was it necessary to use blind seals? Because they______. A. were unable to use sight for clues    B. had better hearing C. were waiting to be fed             D. were the only animals to be found 68. To those seals strong signal meant_____. A. snapping     B. nothing      C. food       D. a light tap 69. The article doesn’t say directly but suggests that fishermen usually think______. A. seals have no good sense of hearing   B. seals have good sense of hearing C. seals can only recognize bell sounds   D. seals can not hear soft or long distant sounds 70. Which title will be the best to suit the article? A. Clever Seals                      B. Smart Learners C. An Underwater School             D. An Unknown School