词组but for有两种意思：
a) 要不是，若非【注意虚拟语气】
- But for your help, I would not have got success.
- But for these interruptions, the meeting would have finished earlier.
- I might never have got to university but for you.
- But for the doctor's expertise, she would have died.
b) 除……以外【=except for (sth)】
- All was silent but for the sound of the wind in the trees.
- The work was now complete, but for a final coat of paint.
