Large scale software development

Hi,
Could some one experienced in large software development using scrum provide explanation why A) and D) are wrong in the question below

Which 2 statements are true regarding the nature of large software development with scrum

a) No addition or changes to the core scrum framework are needed to be successful with scrum at large scale
b) A well structured product catalog can minimize and often eliminate development teams members working on multiple scrum teams during a sprint
c) A single person working on multiple scrum teams is often less productive than one focused on the sprint backlog of a single scrum team
d) For large scale software development, scrum requires having team members be full time on single team

As I understand, scaled scrum is part of core scrum framework and this is what is needed for large scale software development and so a) is true. Also, having someone part time may be similar to someone working on multiple teams (understand that it may not be a case always) and so d) could be true as well.

I see b) and c) as same as both point to one person belonging to one scrum team only.