In which one of the following sentences is but used as a preposition? A. I wanted to leave, but I was embarrassed to do so. B. We discovered that Candy will do anything but work. C. The lake is pretty, but it's too cold for swimming. D. I would like to return to Italy, but I have no money.
B, because in all of the other answers but is used as a conjunction which is why there is a comma.