c.gtld-servers.NET has no CNAME records.
Question and response
Question
dig c.gtld-servers.NET. NS
Answer
The response has no answer records.
Authority
gtld-servers.NET. 10781 SOA av4.nstld.com. nstld.verisign-grs.com. 1771966919 3600 900 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0