Apex domains cannot have CNAME records.
Question and response
Question
dig niobe.100.pt. NS
Answer
niobe.100.pt. 5 NS ns1.easyhost.pt.
niobe.100.pt. 5 NS ns3.easyhost.pt.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0