Hi XiaDeng. I would stick with the example in the first sentence. Your two options might be used and quite commonly in different areas of the US, at least. Keep in mind, however, that English is dynamic and the current trend is definitely word reduction. Think of the text messages, tweets, and even emails that we write with as few words as possible. Additionally, there seems to be more and more emphasis on technical writing as well that encourages a more succinct writing style. But as the speaker or writer, ultimately, you make the choice. :) Hope this helps, e.