Apex domains cannot have CNAME records.
Question and response
Question
dig 21grams.com. NS
Answer
21grams.com. 5 NS ns101.digicertdns.com.
21grams.com. 5 NS ns100.digicertdns.com.
21grams.com. 5 NS ns102.digicertdns.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0