Role of the PMO?

Hello,

I am wondering what is the answer to this question from the Practitioner Open:

Q: Which best describes the role of the PMO in an organization that uses Scrum?

A) There is no role for a PMO in scaled Scrum

B) The PMO may be tasked with higher level optimizations for program and portfolio management, based on effective application of techniques that compliment Scrum

C) The PMO transitions all of its project managers to Product Owner, but other than that, its role does not change

D) The PMO transitions all of its project managers to Scrum Masters, but other that that, it's role does not change

I tried with there is no such role but after that I read some articles (like: http://www.mountaingoatsoftware.com/articles/the-roles-of-the-project-management-office-in-scrum) and now I'm wondering what's the correct answer.

There are some other questions from the Practitioner Open that I'm wondering about because most of the topics are not mentioned in the Scrum Guide or in testmaker. Do we actually need the Practitioner Open to pass PSM 1?

Thanks in advance for all your comments.