Regarding VSAs, which statement is true? 

Answer options:

A. VSAs may be implemented on any RADIUS server.
B. VSAs are proprietary, and therefore may only be used on the RADIUS server of that vendor. For example, a Cisco VSA may only be used on a Cisco RADIUS server, such as ACS or ISE.C. VSAs do not apply to RADIUS; they are a TACACS attribute.
D. Each VSA is defined in an RFC and is considered to be a standard.

A