Apex domains cannot have CNAME records.
Question and response
Question
dig amazon.com. NS
Answer
amazon.com. 3 NS ns1.amzndns.co.uk.
amazon.com. 3 NS ns2.amzndns.org.
amazon.com. 3 NS ns2.amzndns.net.
amazon.com. 3 NS ns1.amzndns.net.
amazon.com. 3 NS ns2.amzndns.co.uk.
amazon.com. 3 NS ns1.amzndns.org.
amazon.com. 3 NS ns2.amzndns.com.
amazon.com. 3 NS ns1.amzndns.com.
Authority
The response has no authority records.
Additional
ns1.amzndns.co.uk. 3 A 156.154.67.10
ns1.amzndns.net. 3 A 156.154.65.10
ns1.amzndns.org. 3 A 156.154.66.10
ns2.amzndns.co.uk. 3 A 204.74.120.1
ns2.amzndns.net. 3 A 156.154.69.10
ns2.amzndns.org. 3 A 156.154.150.1
ns1.amzndns.co.uk. 3 AAAA 2001:502:4612:0:0:0:0:10
ns1.amzndns.net. 3 AAAA 2610:a1:1014:0:0:0:0:10
ns1.amzndns.org. 3 AAAA 2610:a1:1015:0:0:0:0:10
ns2.amzndns.co.uk. 3 AAAA 2610:a1:32d1:0:0:0:0:53
ns2.amzndns.net. 3 AAAA 2610:a1:1017:0:0:0:0:10
ns2.amzndns.org. 3 AAAA 2610:a1:31d1:0:0:0:0:53
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0