Question 6. Choose the correct option for each for each numbered gap in the passage People have used codes to send secret messages since Roman times. But codes are not just something (1) ______ by Julius Caesar or a spy. People today use codes every time they pay for something by credit card or send an email to a friend. Codes (2) ______ our personal information. Before computers, the biggest users of codes were governments, who used them particularly in war. The (3) ______ Greeks sent and received messages using a scytale, a cylinder made of wood. An officer would put cloth around the cylinder and write a message along it. When he took the cloth off, the writing appeared to mean nothing. But the officer who received the cloth had a similar cylinder and could easily read the message. Julius Caesar used a simple system to communicate with his army. (4) ______ writing the letter A, he would write D (+3 letters). Computer security systems today are not so different from the one Caesar used. But the keys are much bigger and there are billions of (5) ______ for each letter or number. 1.A.done B.used C.got D.sent 2.A.protect B.prevent C.defend D.keep 3.A.antique B.early C.old D.ancient 4.A.Because of B.Instead of C.Due to D.Except for 5.A.potentials B.likelihoods C.chances D.possibilities