Apex domains cannot have CNAME records.
Question and response
Question
dig iweb.pl. NS
Answer
iweb.pl. 5 NS dns.iweb.pl.
iweb.pl. 5 NS merkury.perfect.net.pl.
iweb.pl. 5 NS dns.man.bydgoszcz.pl.
Authority
The response has no authority records.
Additional
dns.man.bydgoszcz.pl. 5 A 212.122.200.3
dns.iweb.pl. 5 A 212.122.221.129
merkury.perfect.net.pl. 5 A 185.144.174.1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0