The best answer is C
i The differences between the PBS and the WBS are relatively minor,
but this is not the best answer for the exam. See:
ii The OBS is the document that defines the lines of management
responsibility within the project. The point where the OBS and WBS
intersect is known as a ‘control account’ and defines the manager
responsible for a section of the project work.
iii The BoM only describes the materials used in the work, not the other
elements of the project (eg, labour). The WBS defines all of the work
and consequently all of the costs.