57. From the given options, choose the one which best expresses the given sentence in Indirect/Direct speech: "If you don't keep quiet I will kill you," the thief said to him in a calm voice. a) The thief said calmly that he will kill him if you don't keep quiet. b) The thief said calmly that I will kill you if you don't keep quiet. c) The thief warned him calmly that he would kill him if he didn't keep quiet. d) Calmly the thief warned him that be quiet or else he will have to kill him.​