Apex domains cannot have CNAME records.
Question and response
Question
dig co.zw. NS
Answer
co.zw. 2 NS ns2.liquidtelecom.net.
co.zw. 2 NS ns2.zispa.org.zw.
co.zw. 2 NS ans.dnsstudy.africa.
co.zw. 2 NS ns1.zispa.org.zw.
co.zw. 2 NS ns1.liquidtelecom.net.
Authority
The response has no authority records.
Additional
ans.dnsstudy.africa. 5 A 192.96.24.69
ns1.liquidtelecom.net. 5 A 5.11.11.1
ns2.liquidtelecom.net. 5 A 5.11.11.10
ans.dnsstudy.africa. 5 AAAA 2001:42a0:0:0:0:0:0:69
ns1.liquidtelecom.net. 5 AAAA 2c0f:fe40:0:0:5:11:11:1
ns2.liquidtelecom.net. 5 AAAA 2c0f:fe40:0:0:5:11:11:10
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0