Apex domains cannot have CNAME records.
Question and response
Question
dig kr.ua. NS
Answer
kr.ua. 5 NS ba1.ns.ua.
kr.ua. 5 NS zt.ns.ua.
kr.ua. 5 NS ns.infocom.kr.ua.
kr.ua. 5 NS ns.host.kr.ua.
kr.ua. 5 NS nn.ns.ua.
Authority
The response has no authority records.
Additional
nn.ns.ua. 171771 A 194.58.197.4
ns.host.kr.ua. 5 A 193.23.157.3
ns.infocom.kr.ua. 5 A 195.230.140.2
nn.ns.ua. 171771 AAAA 2a01:3f1:c001:0:0:0:0:53
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0