Apex domains cannot have CNAME records.
Question and response
Question
dig host.bg. NS
Answer
host.bg. 5 NS pns1.host.bg.
host.bg. 5 NS sns1.host.bg.
host.bg. 5 NS sns3.host.bg.
host.bg. 5 NS pns2.host.bg.
host.bg. 5 NS sns2.host.bg.
Authority
The response has no authority records.
Additional
pns1.host.bg. 5 A 195.191.148.253
pns2.host.bg. 5 A 195.191.149.253
sns1.host.bg. 5 A 178.162.131.66
sns2.host.bg. 5 A 81.17.60.30
sns3.host.bg. 5 A 37.48.73.70
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0