When is it possible to use a self-signed certificate, rather than one purchased from a commercial
certificate authority?
C
Explanation:
This can include SSL/TLS certificates, code signing certificates, and S/MIME certificates. The reason
why theyre considered different from traditional certificate-authority signed certificates is that
theyre created, issued, and signed by the company or developer who is responsible for the website
or software being signed. This is why self-signed certificates are considered unsafe for public-facing
websites and applications.
Reference:
https://sectigostore.com/page/what-is-a-self-signed-certificate/
D is the right answer