Apex domains cannot have CNAME records.
Question and response
Question
dig nic.green. NS
Answer
nic.green. 5 NS a2.nic.green.
nic.green. 5 NS c0.nic.green.
nic.green. 5 NS a0.nic.green.
nic.green. 5 NS b0.nic.green.
Authority
The response has no authority records.
Additional
a0.nic.green. 149369 A 65.22.32.9
a2.nic.green. 149369 A 65.22.35.9
b0.nic.green. 149369 A 65.22.33.9
c0.nic.green. 149369 A 65.22.34.9
a0.nic.green. 149369 AAAA 2a01:8840:22:0:0:0:0:9
a2.nic.green. 149369 AAAA 2a01:8840:25:0:0:0:0:9
b0.nic.green. 149369 AAAA 2a01:8840:23:0:0:0:0:9
c0.nic.green. 149369 AAAA 2a01:8840:24:0:0:0:0:9
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0