1. If you are absent-minded in class, you won't learn anything.2. Sorry, what did you say? I was spaced out for a minute here.3. My friend seems upset and distrait; it turns out his dad is seriously sick.
 Absent-minded be spaced out distrait drift offdrift off 很常用， be spaced out 是俚語，也很常用
1. 上課不專心, 你什麼都學不到.2. 不好意思, 你剛剛說什麼? 我突然恍神了一下.3. 我朋友看起來心不在焉的, 原來是因為他爸病重.
It gives the illuion that you've computed the entire answer immediately.