Apex domains cannot have CNAME records.
Question and response
Question
dig giaothongxanh.org. NS
Answer
giaothongxanh.org. 5 NS ns-1387.awsdns-45.org.
giaothongxanh.org. 5 NS ns-834.awsdns-40.net.
giaothongxanh.org. 5 NS ns-1922.awsdns-48.co.uk.
giaothongxanh.org. 5 NS ns-1744.awsdns-26.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0