Apex domains cannot have CNAME records.
Question and response
Question
dig upc.cat. NS
Answer
upc.cat. 5 NS ns1.cesca.cat.
upc.cat. 5 NS ns2.cesca.cat.
upc.cat. 5 NS ns1.upc.edu.
upc.cat. 5 NS ns2.upc.edu.
Authority
The response has no authority records.
Additional
ns1.upc.edu. 2 A 147.83.0.1
ns2.upc.edu. 2 A 147.83.0.2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0