Apex domains cannot have CNAME records.
Question and response
Question
dig md. NS
Answer
md. 5 NS nsb.tld.md.
md. 5 NS nsa.tld.md.
md. 5 NS nsf.dns.md.
md. 5 NS nsc.dns.md.
Authority
The response has no authority records.
Additional
nsa.tld.md. 166842 A 185.108.181.191
nsb.tld.md. 171885 A 185.108.181.192
nsc.dns.md. 171059 A 144.217.93.2
nsf.dns.md. 172054 A 92.222.76.179
nsc.dns.md. 171059 AAAA 2607:5300:201:3100:0:0:0:2f69
nsf.dns.md. 172054 AAAA 2001:41d0:401:3100:0:0:0:7162
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0