Apex domains cannot have CNAME records.
Question and response
Question
dig cv. NS
Answer
cv. 3 NS anyc.dnsnode.net.
cv. 3 NS c.dns.pt.
cv. 3 NS ns.dns.cv.
cv. 3 NS cv01.dns.pt.
Authority
The response has no authority records.
Additional
c.dns.pt. 167592 A 204.61.216.105
ns.dns.cv. 172791 A 41.221.192.220
c.dns.pt. 167592 AAAA 2001:500:14:6105:ad:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0