Apex domains cannot have CNAME records.
Question and response
Question
dig azure-dns-3.cn. NS
Answer
azure-dns-3.cn. 5 NS ns4-201.azure-dns-3.cn.
azure-dns-3.cn. 5 NS ns1-201.azure-dns-3.cn.
azure-dns-3.cn. 5 NS ns2-201.azure-dns-3.cn.
azure-dns-3.cn. 5 NS ns3-201.azure-dns-3.cn.
Authority
The response has no authority records.
Additional
ns1-201.azure-dns-3.cn. 5 A 40.73.192.201
ns2-201.azure-dns-3.cn. 5 A 40.73.194.201
ns3-201.azure-dns-3.cn. 5 A 40.73.196.201
ns4-201.azure-dns-3.cn. 5 A 40.73.198.201
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0