Apex domains cannot have CNAME records.
Question and response
Question
dig marlow.dk. NS
Answer
marlow.dk. 5 NS ns.ie.tuxbox.nu.
marlow.dk. 5 NS spirillen.hulpsystems.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0