except vs except for ....

牛津出版的”Practical English Usage”，就有以下解釋：
１．except 可以帶或不帶for
except (for) 用在概括性的話後面，尤其是用在all, every, no, everything, anybody, nowhere, whole 等概括性詞後面。
　　He ate everything on his plate except (for) the beans.
　　He ate the whole meal, except (for) the beans.
２．except for
　　在其他情況下，我們通常用except for，而不用except。試比較：
　－I've cleaned all the rooms except (for) the bathroom.(在all後面用except也是可以的)
　　I've cleaned the house except for the bathroom.（不能說：...except the bathroom)

　－Nobody came except (for) John and Mary.（用在nobody的後面）
　　Except for John and Mary, nobody came.（用在nobody的前面）

相信這樣解釋很清楚，你必能白！
希望幫到你！

Except and Except For have the same meaning. The only difference is :

When the things after ‘except’ is a plural noun, then you have to use ‘except for’.

Example :

I can answer all the questions except the last one – correct
I can answer all the questions except for the last two – correct

Your question :

I can answer all the questions except for the last – wrong, the last is singular, also wrong because this sentence is not complete. You have to change it to “last one”.

I can answer all the questions except the last – wrong, change to ‘last one’.

I can answer all the questions except for the last one – wrong, because last one is singular.

I can answer all the questions except the last one – correct.