Apex domains cannot have CNAME records.
Question and response
Question
dig nowo.pt. NS
Answer
nowo.pt. 5 NS ns2.netvisao.pt.
nowo.pt. 5 NS ns.netvisao.pt.
Authority
The response has no authority records.
Additional
ns.netvisao.pt. 5 A 213.228.128.5
ns2.netvisao.pt. 5 A 213.228.128.6
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0