I'm really ashamed that i have to ask you a very basic question like this, but I, having studied Chinese for one year, cannot yet figure out the meaning of 了. 我吃了午饭。I ate lunch. 我吃午饭。I eat lunch. However, things do not seem that easy, as I have seen other examples in which 了 is used to express what is just happening. For example, "不贵了!" means "It is not expensive!" . This has nothing to do with what happened in the past, but 了 is used in the sentence. It is really difficult for me to understand the meaning of 了. Is there anyone who kindly explains this question?