"お待たせ！教科書取りに行ってた"
- Thanks for waiting! (待っててくれてありがとう) I went to go get my textbook.
- Sorry to keep you waiting! （待たせてごめん）I had to get my textbook.
短く・とてもカジュアル（上のほうは少しポライトな感じ）
- Sorry to keep you. I went to get my textbook.
- Hey, sorry. I was getting my textbook.
- Sorry, I was getting my textbook. Let's go. (ごめん、教科書取りに行ってた。行こう）
アメリカ合衆国 
