Apex domains cannot have CNAME records.
Question and response
Question
dig cla.edu.do. NS
Answer
cla.edu.do. 4 NS ns3.exclusivehosting.net.
cla.edu.do. 4 NS ns4.exclusivehosting.net.
cla.edu.do. 4 NS ns1.exclusivehosting.net.
cla.edu.do. 4 NS ns2.exclusivehosting.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0