2 layers of randomization

Hello,
Sorry if this is a simple thing to do but I've tried reading up and I am unsure on my best option!
I have a questionnaire where there are 2 blocks of questions (e.g., A & B). Within A & B I have two further blocks (A1, A2, B1, B2).
I want all participants to complete A & B but complete only one of the sub-blocks. I've done this in the image however, I now also need to randomize the order that A and B are presented which I'm struggling with - i.e., some participants see A first and others see B first
e.g., participant 1 = A1 B1, participant 2 = B2 A1, participant 3 = B2 A2 etc.
Can anyone help? Thanks
qualtrics randomization.pdf