Apex domains cannot have CNAME records.
Question and response
Question
dig 51jsg.com. NS
Answer
51jsg.com. 2 NS ns1.51jsg.com.
51jsg.com. 2 NS ns2.51jsg.com.
Authority
The response has no authority records.
Additional
ns1.51jsg.com. 2 A 185.164.139.107
ns2.51jsg.com. 2 A 185.164.139.107
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0