[译] 有少数学生在课堂上总是心不在焉。
[误] A few students always have their heads in the cloud in class.

[正] A few students always have their heads in the clouds in class.
[注] in the clouds 是固定习语，cloud 必须用复数形式，表示“在云层中”，用作比喻意思，指“心不在焉，空想着”。