Apex domains cannot have CNAME records.
Question and response
Question
dig static.uol.com.br. NS
Answer
static.uol.com.br. 5 NS eliot.uol.com.br.
static.uol.com.br. 5 NS borges.uol.com.br.
static.uol.com.br. 5 NS charles.uol.com.br.
Authority
The response has no authority records.
Additional
eliot.uol.com.br. 5 A 172.64.52.216
borges.uol.com.br. 5 A 172.64.53.68
charles.uol.com.br. 5 A 172.64.52.59
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0