Apex domains cannot have CNAME records.
Question and response
Question
dig uiowa.edu. NS
Answer
uiowa.edu. 5 NS dns-ext-lc-1.uiowa.edu.
uiowa.edu. 5 NS dns-ext-itf-1.uiowa.edu.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0