Apex domains cannot have CNAME records.
Question and response
Question
dig uba.ar. NS
Answer
uba.ar. 2 NS dns34.cloudns.net.
uba.ar. 2 NS ns2.uba.ar.
uba.ar. 2 NS ns1.uba.ar.
uba.ar. 2 NS dns31.cloudns.net.
uba.ar. 2 NS dns32.cloudns.net.
uba.ar. 2 NS dns33.cloudns.net.
Authority
The response has no authority records.
Additional
ns1.uba.ar. 2 A 157.92.1.1
ns2.uba.ar. 2 A 157.92.4.1
ns1.uba.ar. 2 AAAA 2001:1318:100c:1:0:0:0:1
ns2.uba.ar. 2 AAAA 2001:1318:100c:4:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0