Apex domains cannot have CNAME records.
Question and response
Question
dig kluwermedia.be. NS
Answer
kluwermedia.be. 5 NS edns9.ultradns.com.
kluwermedia.be. 5 NS edns9.ultradns.biz.
kluwermedia.be. 5 NS edns9.ultradns.org.
kluwermedia.be. 5 NS edns9.ultradns.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0