A wildcard certificate is designed to secure a primary domain and all associated subdomains with a single certificate, leading to a simplified management process and reduced costs. Since the administrator intends to secure various service areas under the same primary domain, this option is both practical and cost-effective. Conversely, a root certificate represents the trust anchor in a public key infrastructure and would not be suitable for this scenario. A self-signed certificate, typically untrusted by browsers, would not be a viable choice for a commercial site looking to establish customer trust. The certificate revocation list (CRL) is not a type of certificate, but rather a database of revoked certificates.