only one answer out of 15 was marked as "correct"! Which is unexpected since even question 12 is marked as incorrect even when using the code given in the video!
I'd suggest consulting the answers chapter in the book. The course is based on a book with the same name (completely free, of course) and with the added bonus of a chapter for answers. However, despite the exercises being largely the same, there might be some misalignment across the two. So, it might be a good idea to open the chapter at hand on the book as well.
All this aside, it usually has been the case for me that I was misinterpreting the question or the exercise and the code I provided was deficient in some way.
