Feedback comes from students who have attended the ATPL exams and remember(sometimes word by word) the questions found on the paper including the 4 possible answers.
They pass the question to the groundschool's instructors who look at the question and try to make sense of it most of the time finding the right answer.
At this point the question is reproposed to students during the course in order for the student to have more chances to know what kind of questions to expect and possibly find the same question on his paper during the actual exam.
I did all my groundschool with BGS.theyr feedback is SUPERB,I passed them all thanks to excellent instructors and excellent feedback.
Just to give you an Idea all the questions that you find on the BGS progress tests are "feedback questions".
Good luck,hope this helps
M.A.