Apex domains cannot have CNAME records.
Question and response
Question
dig cm. NS
Answer
cm. 5 NS ns2.nic.cm.
cm. 5 NS phloem.uoregon.edu.
cm. 5 NS ns-cm.nic.fr.
cm. 5 NS ns1.nic.cm.
cm. 5 NS ns.itu.ch.
cm. 5 NS ns-cm.afrinic.net.
cm. 5 NS auth02.ns.uu.net.
Authority
The response has no authority records.
Additional
ns.itu.ch. 4 A 156.106.192.121
ns1.nic.cm. 167182 A 195.24.205.60
ns2.nic.cm. 167182 A 195.24.205.61
phloem.uoregon.edu. 5 A 128.223.32.35
ns.itu.ch. 4 AAAA 2a00:7580:60:2141:0:0:0:10
phloem.uoregon.edu. 5 AAAA 2001:468:d01:20:0:0:80df:2023
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0