Apex domains cannot have CNAME records.
Question and response
Question
dig nttsmc.com. NS
Answer
nttsmc.com. 5 NS ns10.nttsmc.com.
nttsmc.com. 5 NS ns.mcnet.ad.jp.
nttsmc.com. 5 NS ns2.mcnet.ad.jp.
Authority
The response has no authority records.
Additional
ns.mcnet.ad.jp. 5 A 210.172.32.50
ns2.mcnet.ad.jp. 5 A 210.172.32.132
ns10.nttsmc.com. 5 A 110.5.41.13
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0