Apex domains cannot have CNAME records.
Question and response
Question
dig presco.com.tw. NS
Answer
presco.com.tw. 4 NS ns-1499.awsdns-59.org.
presco.com.tw. 4 NS ns-974.awsdns-57.net.
presco.com.tw. 4 NS ns-315.awsdns-39.com.
presco.com.tw. 4 NS ns-1725.awsdns-23.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0