Apex domains cannot have CNAME records.
Question and response
Question
dig aulavirtualunade.edu.do. NS
Answer
aulavirtualunade.edu.do. 1 NS ns3.digitalocean.com.
aulavirtualunade.edu.do. 1 NS ns1.digitalocean.com.
aulavirtualunade.edu.do. 1 NS ns2.digitalocean.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0