There are four cups on the kitchen table, each with a sentence written on it: the first cup says "All cups are honey water"; the second cup says "This cup is light Saltwater "; the third cup says" this cup is not sugar water "; the fourth cup says" some cups have no honey water ". If only one sentence written on these four cups is true, which of the following must be true? ['The first cup is honey water.', 'Brine in the second cup.', 'The third cup is sugar water.', 'The fourth cup is not honey water.']