Apex domains cannot have CNAME records.
Question and response
Question
dig tznic.or.tz. NS
Answer
tznic.or.tz. 3 NS b.ns.tznic.or.tz.
tznic.or.tz. 3 NS ns2.tznic.or.tz.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0