Apex domains cannot have CNAME records.
Question and response
Question
dig awsdns-cn-51.net. NS
Answer
awsdns-cn-51.net. 5 NS g-ns-2339.awsdns-cn-51.net.
awsdns-cn-51.net. 5 NS g-ns-1173.awsdns-cn-51.net.
awsdns-cn-51.net. 5 NS g-ns-intl-976.awsdns-cn-51.net.
awsdns-cn-51.net. 5 NS g-ns-intl-4015.awsdns-cn-51.net.
awsdns-cn-51.net. 5 NS g-ns-976.awsdns-cn-51.net.
awsdns-cn-51.net. 5 NS g-ns-4015.awsdns-cn-51.net.
Authority
The response has no authority records.
Additional
g-ns-976.awsdns-cn-51.net. 5 A 52.82.179.208
g-ns-1173.awsdns-cn-51.net. 5 A 52.82.180.149
g-ns-2339.awsdns-cn-51.net. 5 A 54.222.33.35
g-ns-4015.awsdns-cn-51.net. 5 A 54.222.39.175
g-ns-intl-976.awsdns-cn-51.net. 5 A 52.46.187.208
g-ns-intl-4015.awsdns-cn-51.net. 5 A 52.46.183.175
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0