Here are two fill-in-the-blank questions in my grammar exercises.
A man is not old ______ regrets take the place of dreams.
Success always hides behind the next corner in the road, so you'll never know how close it lies ______ you turn the corner.
When going through the questions, my classmates argued that before, until, and unless all sounds fine in the sentence. However, only one of them was considered correct, which I couldn't remember clearly.
Would anyone be so kind as to point me the correct answers out and show me why? Thanks in advance!
(*I'm not a native speaker, so sorry for any mistake. )