问题：

[单选] How does using the service password encryption command on a router provide additional security? （）

A . by encrypting all passwords passing through the router
B . by encrypting passwords in the plain text configuration file
C . by requiring entry of encrypted passwords for access to the device
D . by configuring an MD5 encrypted key to be used by routing protocols to validate routing exchanges
E . by automatically suggesting encrypted passwords for use in configuring the router