accidentally show 2 of 4 question groups - by: lepsid

Thank you for this.
As I can see, this function randomly shows one question from any groups. What I want is to randomly show 2 block of questions of 5. So, I have 5 blocks of questions: B1, B2, B3, B4, B5. And in every block I have several questions. I want to randomly show all questions from randomly chosen two blocks.
How can I do it?

Thank you