Apex domains cannot have CNAME records.
Question and response
Question
dig poltava.ua. NS
Answer
poltava.ua. 5 NS ba1.ns.ua.
poltava.ua. 5 NS nn.ns.ua.
poltava.ua. 5 NS sx.ns.ua.
poltava.ua. 5 NS ho1.ns.pl.ua.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0