Apex domains cannot have CNAME records.
Question and response
Question
dig itojun.org. NS
Answer
itojun.org. 5 NS mango.itojun.org.
itojun.org. 5 NS ns-wide.wide.ad.jp.
Authority
The response has no authority records.
Additional
mango.itojun.org. 5 A 210.155.141.200
ns-wide.wide.ad.jp. 2 A 203.178.136.59
mango.itojun.org. 5 AAAA 2001:2f0:0:8800:0:0:1:1
ns-wide.wide.ad.jp. 2 AAAA 2001:200:0:1:0:0:0:f
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0