Apex domains cannot have CNAME records.
Question and response
Question
dig hitech.cz. NS
Answer
hitech.cz. 5 NS ns.nwt.cz.
hitech.cz. 5 NS ns2.nwt.cz.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0