Apex domains cannot have CNAME records.
Question and response
Question
dig smp.edu.do. NS
Answer
smp.edu.do. 5 NS ns-1310.awsdns-35.org.
smp.edu.do. 5 NS ns-1935.awsdns-49.co.uk.
smp.edu.do. 5 NS ns-133.awsdns-16.com.
smp.edu.do. 5 NS ns-537.awsdns-03.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0