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