Which of the following protocols uses TCP instead of UDP and is incompatible with all previous versions?

Which of the following protocols uses TCP instead of UDP and is incompatible with all previous
versions?

A.
TACACS

B.
XTACACS

C.
RADIUS

D.
TACACS+

Explanation:
TACACS+ is not compatible with TACACS and XTACACS, and makes use of TCP.