A、Playback parts. B、Recording mechanism. C、Speakers. D、Headphone. D

To the Sony engineers who designed it, the Walkman was not quite what they wanted. They were aiming for something different—a stereo version of Sony’s Pressman.
    In 1978, Sony engineers started shrinking stereo components. They could fit in playback parts and two tiny speakers, but not the recording mechanism.
    One day Masaru Ibuka, Sony’s co-founder, wandered by and heard the small stereo. He recalled a project being developed elsewhere in the company—lightweight headphones.
    "What if you got rid of the speakers and combined your stereo with the headphones?" asked Ibuka. "The headphones would use less power and increase the quality of the sound.
    Soon the teenagers discovered the new invention. Perfect for sports, small enough to fit into the pocket, the Walkman became a raging success.