How do external applications consume events from Salesforce?

External applications consume events from Salesforce primarily through the CometD protocol, which is the correct option. CometD is an HTTP-based protocol that enables real-time, push-based communication. This is integral for applications that need to receive notifications or updates automatically as they occur in Salesforce.

CometD leverages the Bayeux protocol, which is designed for server-sent events. When an external application subscribes to specific events in Salesforce, it can receive updates in real time without needing to poll continuously for changes. This efficient method allows applications to react swiftly to changes in Salesforce data, improving integration and user experience.

Other options like using the REST API, standard webhooks, or the SOAP API, while they serve different purposes in API interactions with Salesforce, do not specifically facilitate the real-time consumption of events in the same way that CometD does. The REST API and SOAP API are primarily synchronous communication protocols, and standard webhooks would typically require an outbound call rather than a push mechanism for event notifications. Thus, CometD stands out as the optimal choice for real-time event consumption.