Apex domains cannot have CNAME records.
Question and response
Question
dig NIC.RS. NS
Answer
nic.rs. 5 NS h.nic.rs.
nic.rs. 5 NS a.nic.rs.
nic.rs. 5 NS c.nic.rs.
nic.rs. 5 NS l.nic.rs.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0