Have you been to Beijing before?
　　你以前来过北京吗？

　　A: David, have you been to Beijing before?

　　A: 大卫，你以前来过北京吗？

　　B: Yes, I have. Many times.

　　B: 是的，来过。来过很多次。

　　A: Really? You must know it quite well.

　　A: 是吗？你一定非常了解北京。

　　B: Well, I think this is my sixth visit. I get to know it a little bit more each time.

　　B: 哦，我想这是第六次来北京了。我一次比一次更了解它。

　　A: Six tmies! That's a lot. It's nearly your home city!

　　A: 六次！不少啊。差不多成了你的家乡了！

　　Notes:

　　1. To ask someone if they have done something in the past, you can say: Have you been to Beijing before; Have you seen the Great Wall? 如果问某人在过去是否做过某事，你可以说：Have you been to Beijing before? (你以前去过北京吗？); Have you seen the Great Wall? (你见过长城吗？).

　　2. You must know it quite well. You can use this expression you must...when you think something for certain, e.g. after a long busy day: You must be tired. 你一定对它非常了解。当你非常确定某事时，你可以用下面这个表达法：You must...(你一定...), 例如：在某人忙碌了一天之后说：You must be tired (你一定累了)。