Apex domains cannot have CNAME records.
Question and response
Question
dig mctes.pt. NS
Answer
mctes.pt. 5 NS ns03.fccn.pt.
mctes.pt. 5 NS ns01.fccn.pt.
mctes.pt. 5 NS ns02.fccn.pt.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0