Apex domains cannot have CNAME records.
Question and response
Question
dig yongkangonline.com. NS
Answer
yongkangonline.com. 5 NS ns-596.awsdns-10.net.
yongkangonline.com. 5 NS ns-1697.awsdns-20.co.uk.
yongkangonline.com. 5 NS ns-145.awsdns-18.com.
yongkangonline.com. 5 NS ns-1591.awsdns-06.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0