Apex domains cannot have CNAME records.
Question and response
Question
dig clasesonline.edu.do. NS
Answer
clasesonline.edu.do. 5 NS ns-1256.awsdns-29.org.
clasesonline.edu.do. 5 NS ns-174.awsdns-21.com.
clasesonline.edu.do. 5 NS ns-744.awsdns-29.net.
clasesonline.edu.do. 5 NS ns-1619.awsdns-10.co.uk.
Authority
The response has no authority records.
Additional
ns-174.awsdns-21.com. 5 A 205.251.192.174
ns-744.awsdns-29.net. 5 A 205.251.194.232
ns-1256.awsdns-29.org. 5 A 205.251.196.232
ns-1619.awsdns-10.co.uk. 5 A 205.251.198.83
ns-174.awsdns-21.com. 5 AAAA 2600:9000:5300:ae00:0:0:0:1
ns-744.awsdns-29.net. 5 AAAA 2600:9000:5302:e800:0:0:0:1
ns-1256.awsdns-29.org. 5 AAAA 2600:9000:5304:e800:0:0:0:1
ns-1619.awsdns-10.co.uk. 5 AAAA 2600:9000:5306:5300:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0