Apex domains cannot have CNAME records.
Question and response
Question
dig sd.netserwer24.pl. NS
Answer
sd.netserwer24.pl. 5 NS dns3.hitme.net.pl.
sd.netserwer24.pl. 5 NS dns4.hitme.net.pl.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0