(3) Books may be keep for four weeks. (keep 改为 kept,因此处要用被动语态) (全国卷)
(4) …and let you know when the book you want has returned. (returned 之前加 been,因从句意上看,此处要用被动语态) (全国卷)
(5) Uncle Ben will also go back for Christmas. (go 改为 come,由句意可知) (全国卷)
(6) They eager to know everything about China and asked me lots of questions. (eager 前加were,因此处缺谓语动词) (全国卷)