Which of the following parameters should be set in main.cf to enable TLS in Postfix?

The `smtpd_tls_cert_file` parameter specifies the path to the server certificate, `smtpd_tls_key_file` specifies the path to the private key, `smtpd_tls_CAfile` specifies the path to the file containing CA certificates to verify client certificates, and `smtpd_use_tls` (or `smtpd_tls_security_level`) must be set to enable TLS.

`smtpd_tls_pem_file` is not a standard Postfix parameter for a separate certificate and key; typically, a PEM file would contain both, but distinct `_cert_file` and `_key_file` parameters are used for separate files.

Similar to B, `smtpd_tls_pem_file` is not typically used alongside `smtpd_tls_cert_file` as separate parameters for different purposes in this context.

This option includes `smtpd_tls_pem_file`, which is not the correct parameter when `smtpd_tls_cert_file` and `smtpd_tls_key_file` are used for separate certificate and key files.