Apex domains cannot have CNAME records.
Question and response
Question
dig co.tz. NS
Answer
co.tz. 5 NS ns2.tznic.or.tz.
co.tz. 5 NS rip.psg.com.
co.tz. 5 NS ns.anycast.co.tz.
co.tz. 5 NS tz-e.ns.nic.cz.
co.tz. 5 NS fork.sth.dnsnode.net.
Authority
The response has no authority records.
Additional
ns.anycast.co.tz. 160922 A 204.61.216.15
rip.psg.com. 5 A 147.28.0.39
ns.anycast.co.tz. 160922 AAAA 2001:500:14:6015:ad:0:0:1
rip.psg.com. 5 AAAA 2001:418:1:0:0:0:0:39
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0