Hi Tianyu,
Only you can determine if you are ready to take the exam. The Exam Simulator is a great tool to help you make that decision. If you go to the My Statistics page and Exam Feedback tab, you can review scores from others students that have taken the exam and compare with your scores. Just keep in mind that the statistics reflect the first time taking the exams in the Exam Simulator. The second time you take a particular exam in the Exam Simulator, you would expect your score to be higher because you may remember some of the questions and correct answers. Best of luck as you prepare for your exam.