Apex domains cannot have CNAME records.
Question and response
Question
dig cdc.nicusa.com. NS
Answer
cdc.nicusa.com. 5 NS ns2.nicusa.com.
cdc.nicusa.com. 5 NS ns4.nicusa.com.
cdc.nicusa.com. 5 NS ns7.nicusa.com.
cdc.nicusa.com. 5 NS glns-1.cdc.nicusa.com.
Authority
The response has no authority records.
Additional
ns7.nicusa.com. 5 A 206.17.31.81
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0