Apex domains cannot have CNAME records.
Question and response
Question
dig aws.umd.edu. NS
Answer
aws.umd.edu. 5 NS ns-1277.awsdns-31.org.
aws.umd.edu. 5 NS ns-285.awsdns-35.com.
aws.umd.edu. 5 NS ns-864.awsdns-44.net.
aws.umd.edu. 5 NS ns-1841.awsdns-38.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0