Now that you know it is your fault, why don't you apologize to us?
既然你知道是你的错，为什么不向我们道歉呢？
Now that she comes here, let's start the meeting.
既然她到了，我们就开会吧。
Now that you know he is lying, why you still believe him?
既然你知道他在撒谎，为什么还要相信他呢？