Apex domains cannot have CNAME records.
Question and response
Question
dig support.gov.sg. NS
Answer
support.gov.sg. 1 NS ns10.gdnsdef.com.
support.gov.sg. 1 NS a9-65.akam.net.
support.gov.sg. 1 NS ns12.gdnsdef.com.
support.gov.sg. 1 NS ns7.gdnsdef.com.
support.gov.sg. 1 NS ns3.gdnsec.com.
support.gov.sg. 1 NS a1-6.akam.net.
support.gov.sg. 1 NS ns12.gdnsec.com.
support.gov.sg. 1 NS a20-66.akam.net.
support.gov.sg. 1 NS a3-67.akam.net.
support.gov.sg. 1 NS ns9.gdnsec.com.
support.gov.sg. 1 NS a8-64.akam.net.
support.gov.sg. 1 NS a2-65.akam.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0