Why a wing produces lift? there several theories, however I am probably not the best qualified to comment which is most valid. Anyway whichever explanation you believe there will always be someone who can provide a counter argument and this is something that could be discussed forever.
Mingal, the theory the ppl technical exam recognises for wing lift has always been incorrect since ppl training began. The way I approach the subject is to explain this is what you are required to learn for the exam, but please be aware that it isn't strictly correct, but I would avoid explaining any other theory due to the complexity involved and it would just generally confuse the student. I prefer teach to accurate facts rather than just teaching people to pass an exam, but in this instance it is unavoidable.