Apex domains cannot have CNAME records.
Question and response
Question
dig NIC.rs. NS
Answer
nic.rs. 5 NS c.nic.rs.
nic.rs. 5 NS h.nic.rs.
nic.rs. 5 NS l.nic.rs.
nic.rs. 5 NS a.nic.rs.
Authority
The response has no authority records.
Additional
a.nic.rs. 172209 A 91.199.17.59
c.nic.rs. 172209 A 45.142.220.81
h.nic.rs. 172209 A 91.199.17.60
l.nic.rs. 172209 A 194.146.106.114
a.nic.rs. 172209 AAAA 2001:67c:69c:0:0:0:0:59
c.nic.rs. 172209 AAAA 2a0e:dbc0:2:0:0:0:0:81
h.nic.rs. 172209 AAAA 2001:67c:69c:0:0:0:0:60
l.nic.rs. 172209 AAAA 2001:67c:1010:29:0:0:0:53
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0