Which of the following openssl commands generates a certificate signing request (CSR) using the already existing private key contained in the file private/keypair.pem?
A. openssl req -key private/keypair.pem -out req/csr.pem
B. openssl req – new -key private/keypair.pem -out req/csr.pem
C. openssl gencsr -key private/keypair.pem -out req/csr.pem
D. openssl gencsr -new- key private/keypair.pem -out req/csr.pem