11. But for the teacher's explanation, we understood the lesson ( But for + Noun phrase, clause)

12. But for the rain, we wouldn't have a better crop ( But for + Noun phrase, clause)

13. If I were you, I wouldn't buy it ( cho lời khuyên, if ko có thực S + V2/ed, S + would + V)

14. But for your help, I can finish my work ( But for + Noun phrase, clause)

15. Unless they invite me, I won't come ( unless = if not )

Chúc bạn học tốt!

=>

11. But for the teacher's explanation, we wouldn't have understood the lesson.  

12. But for the rain, we would have a better crop.

13. If I were you, I wouldn't buy it.

14.  But for your daily help, I couldn't finish my work. 

15. Unless they invite me, I will not come.

=>

But for/ without: Nếu không vì 

unless = if...not

If I were you -> thường đưa ra lời khuyên.