Which option in the /etc/ntp.

 The server option is used to configure a persistent association with a remote server or peer. It takes an argument that is either a host name or a numeric IP address of the NTP server. The ntpd daemon will periodically send NTP packets to the specified server and adjust the local clock according to the received responses. Multiple server options can be used to specify more than one NTP source. For example, the following lines in the /etc/ntp.conf file configure four external NTP sources:

server 0.asia.pool.ntp.org

server 0.oceania.pool.ntp.org

server 0.europe.pool.ntp.org

server 0.north-america.pool.ntp.org

References: 

https://docs.ntpsec.org/latest/ntp_conf.html

https://vceguide.com/which-option-in-the-etc-ntp-conf-file-specifies-an-external-ntp-source-to-be-queried-for-time-information-2/

https://vceguide.com/which-option-in-the-etcntp-conf-file-specifies-an-external-ntp-source-to-be-queried-for-time-information/