For a router to obtain a certificate from a CA， what is the first stepof the certificate enrollment process？（）

• A、 the router generates a certificate request and forwards it tothe CA
• B、 the router generates an RSA key pair
• C、 the router sends its public key to the CA
• D、 the CA sends its public key to the router
• E、 the CA verifies the identity of the router
• F、 the CA generates a certificate request and forwards it to the router