Apex domains cannot have CNAME records.
Question and response
Question
dig nic.cam. NS
Answer
nic.cam. 2 NS d.nic.cam.
nic.cam. 2 NS c.nic.cam.
nic.cam. 2 NS a.nic.cam.
nic.cam. 2 NS b.nic.cam.
Authority
The response has no authority records.
Additional
a.nic.cam. 131803 A 194.169.218.77
b.nic.cam. 131803 A 185.24.64.77
c.nic.cam. 131803 A 212.18.248.77
d.nic.cam. 131803 A 212.18.249.77
a.nic.cam. 131803 AAAA 2001:67c:13cc:0:0:0:1:77
b.nic.cam. 131803 AAAA 2a04:2b00:13cc:0:0:0:1:77
c.nic.cam. 131803 AAAA 2a04:2b00:13ee:0:0:0:0:77
d.nic.cam. 131803 AAAA 2a04:2b00:13ff:0:0:0:0:77
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0