Which of the following authentication services should be replaced with a more secure alternative?

A.
RADIUS

B.
TACACS

C.
TACACS+

D.
XTACACS

Explanation:
Terminal Access Controller Access-Control System (TACACS) is less secure than XTACACS, which is a proprietary extension of TACACS, and less secure than
TACACS+, which replaced TACACS and XTACACS.
Incorrect Answers:
A, C: TACACS+ and RADIUS have mostly replaced TACACS and XTACACS in modern networks.
D: XTACACS is a proprietary extension of TACACS.

http://en.wikipedia.org/wiki/TACACS