Apex domains cannot have CNAME records.
Question and response
Question
dig cyf-kr.edu.pl. NS
Answer
cyf-kr.edu.pl. 5 NS dns.fuw.edu.pl.
cyf-kr.edu.pl. 5 NS info.cyf-kr.edu.pl.
cyf-kr.edu.pl. 5 NS nms.cyf-kr.edu.pl.
Authority
The response has no authority records.
Additional
dns.fuw.edu.pl. 5 A 193.0.80.11
nms.cyf-kr.edu.pl. 5 A 149.156.1.3
info.cyf-kr.edu.pl. 5 A 149.156.4.11
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0