Apex domains cannot have CNAME records.
Question and response
Question
dig ns05.com. NS
Answer
ns05.com. 5 NS ns02.com.
ns05.com. 5 NS ns05.com.
ns05.com. 5 NS ns01.com.
ns05.com. 5 NS ns03.com.
ns05.com. 5 NS ns04.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0