A、Playing a word game. B、Arguing with each other. C、Whispering to each other. D、Talking about their families. A细节题。根据短文中的because

Conversations are really kind of interesting. I guess it’s a kind of hobby of mine to listen to conversations that I can hear in public. It is amazing how different the style, or the tone or the content of different conversations can be and to listen to the differences in the language that people use when they speak to different people.
    If you’re ever in a bookstore or department store, it’s interesting to hear how the same salesperson talks to different people. There’re other interesting places to listen to conversations too. I think, and one place that I’ve found is on bus trips. People often talk to each other as if no one else were there. I guess they think people can’t hear their conversations.
    Recently I was on a bus, and I was listening to a conversation of two people behind me. I can’t really say I was listening. I guess it would have been hard not to hear it. it was amusing to listen to the two people, though, because they were playing a kind of language, uh, word game about states and state capitals. One person would say the name of the state, and the other person would say the name of the capital.
    It sounds like a kind of simple game that doesn’t involve much language, and you wouldn’t think that it would involve very much conversation, but actually this wasn’t the case because they were playing this game. They continued to compliment one another and talk about how much they knew about history and how many of the other things that they could or couldn’t remember about those places from their trips or from their reading. It was really kind of fun to listen to them.