Apex domains cannot have CNAME records.
Question and response
Question
dig rethink.org. NS
Answer
rethink.org. 5 NS dns0.positive-internet.com.
rethink.org. 5 NS dns1.positive-internet.com.
Authority
The response has no authority records.
Additional
dns0.positive-internet.com. 5 A 80.87.128.65
dns1.positive-internet.com. 5 A 80.87.136.65
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0