Apex domains cannot have CNAME records.
Question and response
Question
dig ctm.net. NS
Answer
ctm.net. 1 NS vassun2.macau.ctm.net.
ctm.net. 1 NS vassun1.macau.ctm.net.
ctm.net. 1 NS ns3.macau.ctm.net.
Authority
The response has no authority records.
Additional
ns3.macau.ctm.net. 1 A 202.175.36.8
vassun1.macau.ctm.net. 1 A 202.175.3.3
vassun2.macau.ctm.net. 1 A 202.175.3.8
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0