c.tld.sk has no CNAME records.
Question and response
Question
dig c.tld.sk. NS
Answer
The response has no answer records.
Authority
tld.sk. 10140 SOA a.tld.sk. hostmaster.sk-nic.sk. 2025011441 28800 7200 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0