Apex domains cannot have CNAME records.
Question and response
Question
dig uncuyo.edu.ar. NS
Answer
uncuyo.edu.ar. 5 NS raiz.uncuyo.edu.ar.
uncuyo.edu.ar. 5 NS zonda.uncuyo.edu.ar.
uncuyo.edu.ar. 5 NS noc.uncuyo.edu.ar.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0