Apex domains cannot have CNAME records.
Question and response
Question
dig spf.rice.edu. NS
Answer
spf.rice.edu. 5 NS ns2.rice.edu.
spf.rice.edu. 5 NS ns1.rice.edu.
Authority
The response has no authority records.
Additional
ns1.rice.edu. 4 A 128.42.209.32
ns2.rice.edu. 4 A 128.42.178.32
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0