Apex domains cannot have CNAME records.
Question and response
Question
dig com.br. NS
Answer
com.br. 3 NS f.dns.br.
com.br. 3 NS c.dns.br.
com.br. 3 NS a.dns.br.
com.br. 3 NS b.dns.br.
com.br. 3 NS d.dns.br.
com.br. 3 NS e.dns.br.
Authority
The response has no authority records.
Additional
a.dns.br. 172342 A 200.219.148.10
b.dns.br. 73369 A 200.189.41.10
c.dns.br. 73369 A 200.192.233.10
d.dns.br. 73369 A 200.219.154.10
e.dns.br. 73369 A 200.229.248.10
f.dns.br. 73369 A 200.219.159.10
a.dns.br. 172342 AAAA 2001:12f8:6:0:0:0:0:10
b.dns.br. 73369 AAAA 2001:12f8:8:0:0:0:0:10
c.dns.br. 73369 AAAA 2001:12f8:a:0:0:0:0:10
d.dns.br. 73369 AAAA 2001:12f8:4:0:0:0:0:10
e.dns.br. 73369 AAAA 2001:12f8:2:0:0:0:0:10
f.dns.br. 73369 AAAA 2001:12f8:c:0:0:0:0:10
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0