听力原文： Japanese-style. conversations develop quite differently from Western-style. conversations. A Western-style. conversation between two people is like a game of tennis. If I introduce a topic, a conversational ball, I expect you to hit it back. If you agree with me, I don't expect you simply to agree and do nothing more . I expect you to add something—a reason for agreeing, or another example to carry the idea further. I am just happy if you question me, or completely disagree with me. Whether you agree or disagree, your response will return the ball to me. A Japanese-style. conversation, however, is like bowling. You wait for your turn. And you always know your place in line. It depends on such things as whether you are older or younger, a close friend or a stranger to the previous speaker, in a senior or junior position, and so on. When your turn comes, you step up to the starting line with your bowling ball and carefully bowl it. Everyone else stands back and watch politely, giving encouragement. Then, after everyone is sure that you have completely finished your turn, the next person in line steps up to the same starting line, with a different ball. Your ball is not returned. What is the main topic of the passage?