Apex domains cannot have CNAME records.
Question and response
Question
dig YANDEX.RU. NS
Answer
YANDEX.RU. 5 NS ns1.YANDEX.RU.
YANDEX.RU. 5 NS ns2.YANDEX.RU.
Authority
The response has no authority records.
Additional
ns1.yandex.RU. 5 A 213.180.193.1
ns2.yandex.RU. 5 A 93.158.134.1
ns1.yandex.RU. 5 AAAA 2a02:6b8:0:0:0:0:0:1
ns2.yandex.RU. 5 AAAA 2a02:6b8:0:1:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0