Apex domains cannot have CNAME records.
Question and response
Question
dig el-libro.org.ar. NS
Answer
el-libro.org.ar. 5 NS gene.ns.cloudflare.com.
el-libro.org.ar. 5 NS rudy.ns.cloudflare.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0