[单项选择]The enable secret password appears as an MD5 hash in a router’s configuration file， whereas the enablepassword is not hashed （or encrypted， if the password-encryption service is not enabled）. What is thereason that Cisco still support the use of both enable secret and enable passwords in a router’sconfiguration？（）
A. The enable password is present for backward compatibility.
B. Because the enable secret password is a hash， it cannot be decrypted. Therefore， the enable password is used to match the password that was entered， and the enable secret is used to verify that the enablepassword has not been modified since the hash was generated.
C. The enable password is considered to be a router’s public key， whereas the enable secret password is considered to be a router’s private key.
D. The enable password is used for IKE Phase I， whereas the enable secret password is used for IKE Phase II.