Apex domains cannot have CNAME records.
Question and response
Question
dig centu.edu.do. NS
Answer
centu.edu.do. 5 NS ns3.contabo.net.
centu.edu.do. 5 NS ns1.contabo.net.
centu.edu.do. 5 NS ns2.contabo.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0