Apex domains cannot have CNAME records.
Question and response
Question
dig greengeeks.net. NS
Answer
greengeeks.net. 5 NS ns2.greengeeks.net.
greengeeks.net. 5 NS ns1.greengeeks.net.
Authority
The response has no authority records.
Additional
ns1.greengeeks.net. 5 A 75.2.69.7
ns2.greengeeks.net. 5 A 99.83.188.187
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0