First round is HR screening, he asked about my background, why I'm interested in this role, and when can I start the job. They seems need peple for start the position immediately

Case study with a current PA. The case study starts out simple but progresses in complexity as more edge cases are thrown in to test your mental framework. I managed to arrive at the correct answer for each question(there is a correct answer for every question despite HR telling you cases are open-ended). You are not allowed to make mistakes in your thinking or say something that is wrong even if you correct your thinking later and achieve consensus with the interviewer. Therefore make your first answer count.