Apex domains cannot have CNAME records.
Question and response
Question
dig multi-n.pl. NS
Answer
multi-n.pl. 4 NS ns3.nazwa.pl.
multi-n.pl. 4 NS ns2.nazwa.pl.
multi-n.pl. 4 NS ns1.nazwa.pl.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0