Apex domains cannot have CNAME records.
Question and response
Question
dig osakidetza.eus. NS
Answer
osakidetza.eus. 4 NS ns-2017.awsdns-60.co.uk.
osakidetza.eus. 4 NS ns-224.awsdns-28.com.
osakidetza.eus. 4 NS ns-847.awsdns-41.net.
osakidetza.eus. 4 NS ns-1531.awsdns-63.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0