Apex domains cannot have CNAME records.
Question and response
Question
dig 0-15.20.97.80.in-addr.arpa. NS
Answer
0-15.20.97.80.in-addr.arpa. 5 NS ns1.radiocom.ro.
0-15.20.97.80.in-addr.arpa. 5 NS ns2.radiocom.ro.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0