Apex domains cannot have CNAME records.
Question and response
Question
dig carnival.com.bd. NS
Answer
carnival.com.bd. 5 NS rodney.ns.cloudflare.com.
carnival.com.bd. 5 NS sandy.ns.cloudflare.com.
Authority
The response has no authority records.
Additional
sandy.ns.cloudflare.com. 2 A 108.162.192.219
sandy.ns.cloudflare.com. 2 A 172.64.32.219
sandy.ns.cloudflare.com. 2 A 173.245.58.219
rodney.ns.cloudflare.com. 2 A 108.162.193.228
rodney.ns.cloudflare.com. 2 A 172.64.33.228
rodney.ns.cloudflare.com. 2 A 173.245.59.228
sandy.ns.cloudflare.com. 2 AAAA 2606:4700:50:0:0:0:adf5:3adb
sandy.ns.cloudflare.com. 2 AAAA 2803:f800:50:0:0:0:6ca2:c0db
sandy.ns.cloudflare.com. 2 AAAA 2a06:98c1:50:0:0:0:ac40:20db
rodney.ns.cloudflare.com. 2 AAAA 2606:4700:58:0:0:0:adf5:3be4
rodney.ns.cloudflare.com. 2 AAAA 2803:f800:50:0:0:0:6ca2:c1e4
rodney.ns.cloudflare.com. 2 AAAA 2a06:98c1:50:0:0:0:ac40:21e4
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0