Apex domains cannot have CNAME records.
Question and response
Question
dig pl.ua. NS
Answer
pl.ua. 5 NS sx.ns.ua.
pl.ua. 5 NS nn.ns.ua.
pl.ua. 5 NS ho1.ns.pl.ua.
pl.ua. 5 NS ba1.ns.ua.
Authority
The response has no authority records.
Additional
nn.ns.ua. 171361 A 194.58.197.4
nn.ns.ua. 171361 AAAA 2a01:3f1:c001:0:0:0:0:53
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0