HTTP status code for unsupported HTTP method is 405 right?
yes that's correct, however it's an open debate whether one should actually use 400, 404 or 405 in these cases - particularly if a service is public-facing. That's why we allow any of the three to be applied.
For Question 5.2, you can choose 400, 404 or 405. You get it correct?
So option 4: None of the above is wrong.
thanks @chesterheng it should be "Any of the above"