当我到家时,我才意识到我把雨伞落在教室里了.
1 Until I got home,I didn't realize that I had left my umbrella in the classroom
2 It was not until I got home that I realized that I had left my umbrella in the classroom
3 Not until I got home did I realize that I had left my umbrella in the classroom.
（英语中的三大句型都给你了.）