Apex domains cannot have CNAME records.
Question and response
Question
dig upenn.edu. NS
Answer
upenn.edu. 5 NS adns4.upenn.edu.
upenn.edu. 5 NS adns2.nnn.upenn.edu.
upenn.edu. 5 NS dns2.udel.edu.
upenn.edu. 5 NS adns1.nnn.upenn.edu.
upenn.edu. 5 NS dns1.udel.edu.
upenn.edu. 5 NS adns5.upenn.edu.
upenn.edu. 5 NS adns6.upenn.edu.
upenn.edu. 5 NS adns3.nnn.upenn.edu.
Authority
The response has no authority records.
Additional
dns1.udel.edu. 5 A 128.175.13.16
dns2.udel.edu. 5 A 128.175.13.17
adns1.nnn.upenn.edu. 5 A 128.91.2.53
adns2.nnn.upenn.edu. 5 A 128.91.254.53
adns3.nnn.upenn.edu. 5 A 128.91.251.53
adns4.upenn.edu. 5 A 208.94.148.32
adns5.upenn.edu. 5 A 208.80.124.32
adns6.upenn.edu. 5 A 208.80.126.32
adns1.nnn.upenn.edu. 5 AAAA 2607:f470:1001:0:0:0:ad:1
adns2.nnn.upenn.edu. 5 AAAA 2607:f470:1002:0:0:0:ad:2
adns3.nnn.upenn.edu. 5 AAAA 2607:f470:1003:0:0:0:ad:3
adns4.upenn.edu. 5 AAAA 2600:1800:5:0:0:0:1:0
adns5.upenn.edu. 5 AAAA 2600:1801:6:0:0:0:1:0
adns6.upenn.edu. 5 AAAA 2600:1802:7:0:0:0:1:0
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0