Apex domains cannot have CNAME records.
Question and response
Question
dig csuc.cat. NS
Answer
csuc.cat. 1 NS ns2.csuc.cat.
csuc.cat. 1 NS ns1.csuc.cat.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0