Sorry,I was preoccupied.
→미안해,잠시 딴생각했었어.

〔 예문 〕

A : Ms. Smith are you listenig to me?
    스미스부인 제얘기듣고있나요?

B: Sorry. What did you say? I was preoccupied.
   미안해요.뭐라고 하셨죠? 잠시 딴생각했었어요.

※pre (미리,전에의뜻) + occupied (차지하고있는)=preoccupied(미리차지하고있는)