Apex domains cannot have CNAME records.
Question and response
Question
dig delta.com. NS
Answer
delta.com. 2 NS ns93.ultradns2.com.
delta.com. 2 NS edns2.ultradns.org.
delta.com. 2 NS edns2.ultradns.biz.
delta.com. 2 NS edns2.ultradns.com.
delta.com. 2 NS edns2.ultradns.net.
delta.com. 2 NS ns93.ultradns2.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0