Apex domains cannot have CNAME records.
Question and response
Question
dig access.hol.gr. NS
Answer
access.hol.gr. 5 NS ns1.hol.gr.
access.hol.gr. 5 NS ns0.hol.gr.
access.hol.gr. 5 NS ns2.hol.gr.
Authority
The response has no authority records.
Additional
ns0.hol.gr. 5 A 194.30.220.110
ns1.hol.gr. 5 A 194.30.220.119
ns2.hol.gr. 5 A 194.30.220.118
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0