Apex domains cannot have CNAME records.
Question and response
Question
dig ns1.omro.host. NS
Answer
ns1.omro.host. 5 NS ns1.zomro.net.
ns1.omro.host. 5 NS ns2.zomro.ru.
ns1.omro.host. 5 NS ns3.zomro.com.
ns1.omro.host. 5 NS ns4.zomro.su.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0