Jack said he_____(return) the two books to the library in a week.
Jack said he ( would return ) the two books to the library in a week.为什么啊，过去将来吗？一般过去，returned不行吗？是的。in a week是将来时间，return 受主句谓语动词 said(过去时的制约)，宾语从句要用过去时态的某种形式，在此需要用过去将来时 would return