Apex domains cannot have CNAME records.
Question and response
Question
dig sprint.com.pl. NS
Answer
sprint.com.pl. 5 NS ns2.sprintdatacenter.pl.
sprint.com.pl. 5 NS ns1.sprintdatacenter.pl.
Authority
The response has no authority records.
Additional
ns1.sprintdatacenter.pl. 5 A 46.29.17.41
ns2.sprintdatacenter.pl. 5 A 89.191.144.119
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0