Apex domains cannot have CNAME records.
Question and response
Question
dig static.netgroup.dk. NS
Answer
static.netgroup.dk. 4 NS authns2.ngdc.net.
static.netgroup.dk. 4 NS authns1.ngdc.net.
Authority
The response has no authority records.
Additional
authns1.ngdc.net. 4 A 217.30.38.181
authns2.ngdc.net. 4 A 217.30.38.27
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0