Apex domains cannot have CNAME records.
Question and response
Question
dig terra.com.br. NS
Answer
terra.com.br. 4 NS a28-64.akam.net.
terra.com.br. 4 NS a6-66.akam.net.
terra.com.br. 4 NS d.dns.terra.com.br.
terra.com.br. 4 NS a1-19.akam.net.
terra.com.br. 4 NS b.dns.terra.com.br.
terra.com.br. 4 NS a24-67.akam.net.
terra.com.br. 4 NS a11-66.akam.net.
terra.com.br. 4 NS a13-65.akam.net.
Authority
The response has no authority records.
Additional
b.dns.terra.com.br. 4 A 193.108.91.19
d.dns.terra.com.br. 4 A 2.16.130.67
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0