Apex domains cannot have CNAME records.
Question and response
Question
dig gds.alibabadns.com. NS
Answer
gds.alibabadns.com. 5 NS gdsns2.alibabadns.com.
gds.alibabadns.com. 5 NS gdsns1.alibabadns.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0