Apex domains cannot have CNAME records.
Question and response
Question
dig colegioclaret.edu.do. NS
Answer
colegioclaret.edu.do. 5 NS ns1.a2hosting.com.
colegioclaret.edu.do. 5 NS ns3.a2hosting.com.
colegioclaret.edu.do. 5 NS ns2.a2hosting.com.
colegioclaret.edu.do. 5 NS ns4.a2hosting.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0