Apex domains cannot have CNAME records.
Question and response
Question
dig abac.com. NS
Answer
abac.com. 4 NS ns1.abac.com.
abac.com. 4 NS ns2.abac.com.
Authority
The response has no authority records.
Additional
ns1.abac.com. 4 A 64.29.144.70
ns2.abac.com. 4 A 64.29.154.70
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0