Apex domains cannot have CNAME records.
Question and response
Question
dig rs. NS
Answer
rs. 5 NS h.nic.rs.
rs. 5 NS f.nic.rs.
rs. 5 NS c.nic.rs.
rs. 5 NS a.nic.rs.
rs. 5 NS b.nic.rs.
rs. 5 NS l.nic.rs.
Authority
The response has no authority records.
Additional
a.nic.rs. 143421 A 91.199.17.59
b.nic.rs. 146153 A 195.178.32.2
c.nic.rs. 143421 A 45.142.220.81
f.nic.rs. 34326 A 204.61.216.32
h.nic.rs. 143421 A 91.199.17.60
l.nic.rs. 143421 A 194.146.106.114
a.nic.rs. 143421 AAAA 2001:67c:69c:0:0:0:0:59
b.nic.rs. 146153 AAAA 2a00:e90:0:3:0:0:0:3
c.nic.rs. 143421 AAAA 2a0e:dbc0:2:0:0:0:0:81
f.nic.rs. 34326 AAAA 2001:500:14:6032:ad:0:0:1
h.nic.rs. 143421 AAAA 2001:67c:69c:0:0:0:0:60
l.nic.rs. 143421 AAAA 2001:67c:1010:29:0:0:0:53
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0