Apex domains cannot have CNAME records.
Question and response
Question
dig th.com. NS
Answer
th.com. 5 NS ns1.ksc.net.
th.com. 5 NS ns2.ksc.net.
th.com. 5 NS ns-v6.ksc.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0