Apex domains cannot have CNAME records.
Question and response
Question
dig task.gda.pl. NS
Answer
task.gda.pl. 5 NS ns1.task.gda.pl.
task.gda.pl. 5 NS ns3.task.gda.pl.
task.gda.pl. 5 NS ns2.task.gda.pl.
task.gda.pl. 5 NS rose.man.poznan.pl.
Authority
The response has no authority records.
Additional
ns1.task.gda.pl. 4 A 153.19.250.101
ns2.task.gda.pl. 4 A 212.77.96.123
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0