Apex domains cannot have CNAME records.
Question and response
Question
dig us. NS
Answer
us. 5 NS f.cctld.us.
us. 5 NS w.cctld.us.
us. 5 NS b.cctld.us.
us. 5 NS y.cctld.us.
us. 5 NS k.cctld.us.
us. 5 NS n.cctld.us.
us. 5 NS m.cctld.us.
us. 5 NS x.cctld.us.
Authority
The response has no authority records.
Additional
b.cctld.us. 168476 A 156.154.125.70
f.cctld.us. 169136 A 209.173.58.70
k.cctld.us. 168520 A 156.154.128.70
m.cctld.us. 169136 A 204.74.105.1
n.cctld.us. 169136 A 204.74.107.1
w.cctld.us. 169136 A 37.209.192.15
x.cctld.us. 169136 A 37.209.194.15
y.cctld.us. 169136 A 37.209.196.15
b.cctld.us. 168476 AAAA 2001:502:ad09:0:0:0:0:29
f.cctld.us. 169136 AAAA 2001:500:3682:0:0:0:0:11
k.cctld.us. 168520 AAAA 2001:503:e239:0:0:0:3:1
m.cctld.us. 169136 AAAA 2610:a1:3180:0:0:0:0:53
n.cctld.us. 169136 AAAA 2610:a1:3280:0:0:0:0:53
w.cctld.us. 169136 AAAA 2001:dcd:1:0:0:0:0:15
x.cctld.us. 169136 AAAA 2001:dcd:2:0:0:0:0:15
y.cctld.us. 169136 AAAA 2001:dcd:3:0:0:0:0:15
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0