Apex domains cannot have CNAME records.
Question and response
Question
dig nask.org.pl. NS
Answer
nask.org.pl. 5 NS bilbo.nask.pl.
nask.org.pl. 5 NS kirdan.nask.pl.
nask.org.pl. 5 NS dns.fuw.edu.pl.
nask.org.pl. 5 NS eomer.nask.pl.
Authority
The response has no authority records.
Additional
dns.fuw.edu.pl. 5 A 193.0.80.11
bilbo.nask.pl. 5 A 195.187.245.51
eomer.nask.pl. 5 A 193.59.201.24
kirdan.nask.pl. 5 A 195.187.244.8
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0