Questions 15 to 17 are based on the following passage. At the end of the passage, you will be giv. en 15 seconds to answer the questions. Now, listen to the passage. What suggestions did the experts offer to stereo manufacturers
A．Providing a warning light when the sound is too loud. B．Improving the quality of personal stereo systems. C．Standard hearing test should be set up. D．Restricting the use of personal systems.