The interpretational PMP question section of this article will help you with SPI:
www.project-management-prepcast.com/pmp-exam-questions
There is a worked example. I'm not sure what you mean by 'critical path SPI' as something different from SPI. Perhaps someone else can shed some light on that. Did you mean CPI?
As for the question about holidays, in the real world, any one of those options would be OK. You'd make the decision based on what was best for the project and the team at the time. Where did this question come from? Without more context I can't tell you what the "right" answer is, but perhaps someone with a better memory of the contents of the PMBOK(R) Guide can point us to where that would be covered in the text.