Apex domains cannot have CNAME records.
Question and response
Question
dig OPTORG.RU. NS
Answer
OPTORG.RU. 5 NS ns3.OPTORG.RU.
OPTORG.RU. 5 NS ns1.OPTORG.RU.
OPTORG.RU. 5 NS ns2.OPTORG.RU.
OPTORG.RU. 5 NS ns4.OPTORG.RU.
Authority
The response has no authority records.
Additional
ns3.OPTORG.RU. 5 A 194.85.62.109
ns4.OPTORG.RU. 5 A 194.85.62.110
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0