An agnostic is someone who believes that the existence of God or the supernatural is unknown or unknowable, often expressing doubt or scepticism about religious beliefs. Although option D is the definition of an atheist, it is the best answer to this question. It is important to note that while atheists specifically assert that there is no God or gods, both do not believe in the existence of God or gods. Agnostics just emphasise the lack of knowledge about God's existence, whereas atheists outright deny the existence of God.