Apex domains cannot have CNAME records.
Question and response
Question
dig 151.66.202.in-addr.arpa. NS
Answer
151.66.202.in-addr.arpa. 1 NS ns1.diyixian.com.
151.66.202.in-addr.arpa. 1 NS ns2.diyixian.com.
Authority
The response has no authority records.
Additional
ns1.diyixian.com. 1 A 202.134.93.30
ns2.diyixian.com. 1 A 202.134.64.3
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0