Apex domains cannot have CNAME records.
Question and response
Question
dig 239.75.119.in-addr.arpa. NS
Answer
239.75.119.in-addr.arpa. 4 NS ns3.bit-isle.co.jp.
239.75.119.in-addr.arpa. 4 NS ns2.bit-isle.co.jp.
Authority
The response has no authority records.
Additional
ns2.bit-isle.co.jp. 4 A 61.117.207.3
ns3.bit-isle.co.jp. 4 A 202.131.202.4
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0