Apex domains cannot have CNAME records.
Question and response
Question
dig fuw.edu.pl. NS
Answer
fuw.edu.pl. 5 NS dns.fuw.edu.pl.
fuw.edu.pl. 5 NS dns2.fuw.edu.pl.
fuw.edu.pl. 5 NS ns1.uw.edu.pl.
Authority
The response has no authority records.
Additional
dns.fuw.edu.pl. 5 A 193.0.80.11
ns1.uw.edu.pl. 5 A 193.0.94.133
dns2.fuw.edu.pl. 5 A 193.0.80.12
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0