Apex domains cannot have CNAME records.
Question and response
Question
dig registro.BR. NS
Answer
registro.br. 5 NS b.dns.br.
registro.br. 5 NS d.dns.br.
registro.br. 5 NS c.dns.br.
registro.br. 5 NS a.dns.br.
registro.br. 5 NS e.dns.br.
Authority
The response has no authority records.
Additional
a.dns.br. 56166 A 200.219.148.10
b.dns.br. 74369 A 200.189.41.10
c.dns.br. 70984 A 200.192.233.10
d.dns.br. 74207 A 200.219.154.10
e.dns.br. 66757 A 200.229.248.10
a.dns.br. 56166 AAAA 2001:12f8:6:0:0:0:0:10
b.dns.br. 74369 AAAA 2001:12f8:8:0:0:0:0:10
c.dns.br. 70984 AAAA 2001:12f8:a:0:0:0:0:10
d.dns.br. 74207 AAAA 2001:12f8:4:0:0:0:0:10
e.dns.br. 66757 AAAA 2001:12f8:2:0:0:0:0:10
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0