영어 문법 문제 질문드려요

People in some societies __________ you may marry more than one time.
The Olympic Games have grown from a one-day affair to __________ sixteen days each time it is held.
두 문제는 해설을 봐도 잘 모르겠어요.
그리고 Limiting the number of full-time employees who we have to pay benefits for, and using more part-time people should reduce expenses considerably and increase profits.에서 should가 맞는지도 궁금합니다.