Apex domains cannot have CNAME records.
Question and response
Question
dig psg.edu.do. NS
Answer
psg.edu.do. 3 NS dns2.midominio.do.
psg.edu.do. 3 NS dns4.midominio.do.
psg.edu.do. 3 NS dns1.midominio.do.
psg.edu.do. 3 NS dns3.midominio.do.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0