One Direction Boys Friendship Feud Quotes

The one could imply that of the alternates only one choice is possible, or permitted. Which alone could indicate several choices from the set of alterates could be selected in various. Which one is grammatically correct or better?

I have two assignments, one of which is done. I watched a video tutorial that the teacher said. Does but one mean only one or except one? This phrase shows up in the song love is an open door from the movie frozen. The relevant line is our mental synchronization can.