Agree with Markus. Nothing is tough if you understand the core concepts from grass root level and even simple things are tough if we do not understand them. To my knowledge PMI would not see any section and frame complex question. Question selection is done random for every users from all aspects. You may see complex and confusing questions from any section/line of PMBOK. When you read books, try to read a paragraph and visualize that from some incidences in real life and believe me you are done reading. PMP exam questions are framed keeping real project situations and hence your reading contributes to just small factor, what matters more is your common sense, understanding at core level and visualization of situation in real life.

Rohit, PMP