Hi,
I would not limit the study of the PMBOK Guide based on which questions may end up in the exam.
The first three chapters are crucial for our profession, while I understand - depending on the professional experience - you may already be extremely familiar with the concepts discussed there.
There are many things that can be tested in the exam based on the knowledge from these first chapters; some of them may be pure knowledge-based questions, while others may be situational questions that require the candidate to be familiar with concepts discussed in different chapters.
So I highly recommend to study the whole PMBOK Guide.
Gabriella