Apex domains cannot have CNAME records.
Question and response
Question
dig uoc.edu. NS
Answer
uoc.edu. 5 NS ns-1381.awsdns-44.org.
uoc.edu. 5 NS ns-1588.awsdns-06.co.uk.
uoc.edu. 5 NS ns-142.awsdns-17.com.
uoc.edu. 5 NS ns-620.awsdns-13.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0