In fact the problem is that it is an exercise only with letters useful for the students used to non alphabetical signs in their everyday life.
Here you must add exercises about English vocabulary, grammar or comprehension. So you can add exercises with missing letters, crosswords with definitions or pictures, some English text with questions about it...
These are only few examples of what you can do.
So if you COMPLETE your recognition Roman letters with some more exercises it will be ok. Don�t forget to specify that in your presentation of the document you want to upload.
Good luck !