What is the command to authenticate an NTP time source? (something in those lines)

A.
#ntp authentication-key 1 md5 141411050D 7

B.
#ntp authenticate

C.
#ntp trusted-key 1

D.
#ntp trusted-key 1

Explanation:
The command “ntp authenticate” authenticates the time source.
The command “ntp authentication-key” is the authentication key for trusted time sources.
See the following from a live router:
R1(config)# ntp ?
access-group Control NTP access
allow Allow processing of packets
authenticate Authenticate time sources
authentication-key Authentication key for trusted time sources