Apex domains cannot have CNAME records.
Question and response
Question
dig internuvem.usp.br. NS
Answer
internuvem.usp.br. 1 NS a.dns.usp.br.
internuvem.usp.br. 1 NS c.dns.usp.br.
internuvem.usp.br. 1 NS b.dns.usp.br.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0