Apex domains cannot have CNAME records.
Question and response
Question
dig webcerta.net.br. NS
Answer
webcerta.net.br. 5 NS ns1.w3connect.com.br.
webcerta.net.br. 5 NS ns2.w3connect.com.br.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0