How does Gateway implement Transparent Authentication?

A.
When a user does not have to explicitly connect to the Gateway to perform the authentication before continuing to the destination

B.
When a user authenticated for FTP, HTTP, RLOGIN and TELNET at the same time

C.
When a user have to explicitly connect to the Gateway Module to perform the authentication before continuing to the destination

D.
When a user have to directly connect to the Gateway to perform the authentication before continuing to the destination

E.
When a user authenticated to FTP service only