I just took the exam, and I did not experience too many questions like this - intentionally tricky. But if you choose the BEST answer, it is "b". The WBS may logically be part of the scope baseline, but it is NOT part of the PMBOK def. of the scope baseline.
If you UNDERSTAND how the ITTO's work, you do not need to memorize them - at least that is my experience.
Training for Project Management Professional (PMP)®, PMI Agile Certified Practitioner (PMI-ACP)®, and Certified Associate in Project Management (CAPM)®