Apex domains cannot have CNAME records.
Question and response
Question
dig zone.tc. NS
Answer
zone.tc. 5 NS ns4.nic.tc.
zone.tc. 5 NS ns3.nic.tc.
zone.tc. 5 NS ns1.nic.tc.
zone.tc. 5 NS ns2.nic.tc.
Authority
The response has no authority records.
Additional
ns1.nic.tc. 5 A 95.173.188.29
ns2.nic.tc. 5 A 95.173.177.167
ns3.nic.tc. 5 A 31.169.81.210
ns4.nic.tc. 5 A 217.154.216.152
ns4.nic.tc. 5 AAAA 2a01:239:255:803:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0