You are welcome to answer questions posted in the Ask a Teacher forum as long as your suggestions, help, and advice reflect a good understanding of the English language. If you are not a teacher, you will need to state that clearly at the top of your post. Please note, all posts are moderated by our in-house language experts, so make sure your suggestions, help, and advice house the kind of information an international language teacher would offer. If not, and your posts do not contribute to the topic in a positive way, they will be subject to deletion.
The refugees continued to feel unsafe until they had crossed the border
My teacher corrected the answer using Not until
Not until the refugees had crossed the border, did they feel safe Why we have to change it from 'safe" to unsafe?
The original sentence describes how the refugees felt before they crossed the border.
Your teacher's version describes how the refugess felt after they crossed the border.
Notice how in each sentence there is one negative. In your version, the negative is the "un" in "unsafe"; in the teacher's version, the negative is the word "not".
Not until 
Linear Mode
