Apex domains cannot have CNAME records.
Question and response
Question
dig luotianyi.us. NS
Answer
luotianyi.us. 5 NS ilem.ns.luotianyi.us.
luotianyi.us. 5 NS copy.ns.luotianyi.us.
Authority
The response has no authority records.
Additional
copy.ns.luotianyi.us. 5 A 91.200.176.1
ilem.ns.luotianyi.us. 5 A 109.104.147.1
copy.ns.luotianyi.us. 5 AAAA 2400:52e0:fff0:0:0:0:0:1
ilem.ns.luotianyi.us. 5 AAAA 2400:52e0:fff2:0:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0