Apex domains cannot have CNAME records.
Question and response
Question
dig ifsc.usp.br. NS
Answer
ifsc.usp.br. 1 NS b.dns.usp.br.
ifsc.usp.br. 1 NS a.dns.usp.br.
ifsc.usp.br. 1 NS deneb.ifsc.usp.br.
ifsc.usp.br. 1 NS vega.ifsc.usp.br.
ifsc.usp.br. 1 NS c.dns.usp.br.
Authority
The response has no authority records.
Additional
a.dns.usp.br. 1 A 200.144.248.208
b.dns.usp.br. 1 A 200.144.249.208
c.dns.usp.br. 1 A 177.90.0.18
vega.ifsc.usp.br. 1 A 143.107.229.4
deneb.ifsc.usp.br. 1 A 143.107.228.5
a.dns.usp.br. 1 AAAA 2001:12d0:c000:0:0:0:0:208
b.dns.usp.br. 1 AAAA 2001:12d0:c080:0:0:0:0:208
deneb.ifsc.usp.br. 1 AAAA 2001:12d0:2040:228:0:0:0:5
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0