Apex domains cannot have CNAME records.
Question and response
Question
dig amu.edu.pl. NS
Answer
amu.edu.pl. 5 NS dns2.amu.edu.pl.
amu.edu.pl. 5 NS dns.amu.edu.pl.
amu.edu.pl. 5 NS dns3.amu.edu.pl.
Authority
The response has no authority records.
Additional
dns.amu.edu.pl. 5 A 150.254.65.21
dns2.amu.edu.pl. 5 A 150.254.65.22
dns3.amu.edu.pl. 5 A 164.132.111.99
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0