ncopenbook.gov has no CNAME records.
Question and response
Question
dig ncopenbook.gov. NS
Answer
The response has no answer records.
Authority
gov. 300 SOA a.ns.gov. dns.cloudflare.com. 1771859105 3600 900 604800 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0