Apex domains cannot have CNAME records.
Question and response
Question
dig pbworks.com. NS
Answer
pbworks.com. 4 NS ns-441.awsdns-55.com.
pbworks.com. 4 NS ns-1805.awsdns-33.co.uk.
pbworks.com. 4 NS ns-1083.awsdns-07.org.
pbworks.com. 4 NS ns-693.awsdns-22.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0