ns1.pearson.com has no CNAME records.
Question and response
Question
dig ns1.pearson.com. NS
Answer
The response has no answer records.
Authority
pearson.com. 781 SOA dns-apac-1.ptns.pearson.com. gns-dnsoperations.pearson.com. 2013052593 900 900 2592000 900
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0