Here's an example.
If you want to get a PC and you don’t know from which one to choose, choose something simple.
It doesn't look consistent logically, but another person insists this is the correct form. I find it irregular because it's not exactly a choice if there is only one of... well, anything to choose from.
Is that phrase really better than either of the following examples?
If you want to get a PC and you don’t know which one to choose, choose something simple.
or
If you want to get a PC and you don’t know from which to choose, choose something simple.