Apex domains cannot have CNAME records.
Question and response
Question
dig rau.edu.uy. NS
Answer
rau.edu.uy. 5 NS seciu.edu.uy.
rau.edu.uy. 5 NS ultra.edu.uy.
Authority
The response has no authority records.
Additional
seciu.edu.uy. 5 A 164.73.128.5
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0