Unit 5 - Secret Codes

Secret codes zre an important part of modern life, particularly. When we use e-mail or surfing some webside, we need to key in passwords, and then the system allowed you to use it. Our life is surrounded with secret codes. For exemple, if you want to get the money from the machine, you need to key in passwords. But, too many passwords we sould remember, so sometimes we forget it. It's cumbersome.