Answer:
D. CSR
Explanation:
CSR stands for certificate signing request. It is also known as certification request.
It is a message send to the security certificate authority where the applicant applies for the digital identity certificate. The certificate signing request consists the public key of the applicant. It contains the main information including the digital signature, the domain name, etc.
Thus the administrator should submit the CSR or the certificate signing request in order to receive a new certificate.