why we not use" bằng" ?
Some of the questions have no audio until you click on the discussion. Is this intentional so that we can get practice reading, too?
No. I think that's a technical issue. If you encounter this several times you can submit a bug report.
My vietnam lexicon is not rich enough. I can not understand what is bằng. Why my answer Nói xin lỗi tiếng Anh is marked wrong? What is the difference in using "bằng tiếng Anh" and "tiếng Anh"?
in English = bằng/trong tiếng Anh