Apex domains cannot have CNAME records.
Question and response
Question
dig lrn.com. NS
Answer
lrn.com. 3 NS udns1.ultradns.net.
lrn.com. 3 NS udns2.ultradns.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0