Apex domains cannot have CNAME records.
Question and response
Question
dig planeta.tc. NS
Answer
planeta.tc. 5 NS ns2.extrim.ru.
planeta.tc. 5 NS ns1.extrim.ru.
planeta.tc. 5 NS ns0.extrim.ru.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0