Apex domains cannot have CNAME records.
Question and response
Question
dig dujiangyanren.com. NS
Answer
dujiangyanren.com. 5 NS ns-1564.awsdns-03.co.uk.
dujiangyanren.com. 5 NS ns-1039.awsdns-01.org.
dujiangyanren.com. 5 NS ns-513.awsdns-00.net.
dujiangyanren.com. 5 NS ns-1997.awsdns-57.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0