Anna,
You have two options:
1. If you start Exam 1 - Exam 8, then you will be presented with 200 questions that are selected to simulate the real exam experience. You cannot choose anything.
2. If you start a Quiz (see below the list of exams) then you can select exactly how many questions and from which area/domain you want them.
Please note that both 1 and 2 take the questions from the same pool of 1,600 questions. So if you answer 1,000 questions using option 2 and then start Exam 4, you will most likely see some of the same questions again.