Correct Option: C

puzzle (Noun) : a game; something that is difficult to understand or explain paradox (Noun) : a person, thing or situation that has two opposite features and therefore seems strange; a statement containing two opposite ideas that make it seem impossible paradise (Noun) : a perfect place where people are said to go when they die question (Noun) : a sentence, phrase or word that asks for information challenge (Noun) : a new or difficult task that tests somebody’s ability and skill