Beta version - A development status given to a program or application that contains most of the major features, but is not yet complete.
This course isn't going to have every detail added yet. You also don't need to comment this; we can all tell there is no audio. Report it if you must, but the audio will be added for the final version.
I know that the course is in Beta. But the point of a beta release is to report problems. In other courses this was a real bug, but I was just told, that in this course it might just be like that with some sentences, as they are not TTS but recordings. As I didn't have that information before, I thought it to be a bug, like in any other beta course I used before.