When users report SSO login errors, Login History is the first Salesforce-native place to look for the failure details. It records authentication attempts, statuses, timestamps, source information, and failure reasons that help narrow down whether the problem lies in the identity provider, the assertion, or the Salesforce configuration. Setup Audit Trail is for admin changes, not runtime authentication troubleshooting, and exception email is not the primary way to debug SSO. The practical reason architects start with Login History is that it tells you what Salesforce actually received and how Salesforce evaluated it. That makes it a reliable first checkpoint during alumni portal, workforce SSO, or community login investigations. This is why option C is the best answer in Salesforce terms.