A is correct because defining a new platform event in Salesforce and publishing it with Process Builder when the opportunity status changes to Closed-Won is a valid way to trigger an integration with the ESB using the CometD protocol.
D is correct because enabling ESB to subscribe to the platform event using the CometD protocol and notifying the back-end ERP system to create the order asynchronously is a valid way to handle the integration with the ERP system using a publish-subscribe model.
B is incorrect because publishing to a platform event using the CometD protocol requires an Apex trigger, not a Process Builder process. Also, creating the order synchronously would not be advisable as it would introduce latency and dependency on the ERP system's availability.
C is incorrect because defining a new platform event in the back-end system for the order details would not be possible as platform events are Salesforce-specific objects that can only be defined within Salesforce.
Reference:
1: https://developer.salesforce.com/docs/atlas.en-us.platform_events.meta/platform_events/platform_events_intro_emp.htm
2: https://developer.salesforce.com/docs/atlas.en-us.platform_events.meta/platform_events/platform_events_subscribe.htm
3: https://developer.salesforce.com/docs/atlas.en-us.platform_events.meta/platform_events/platform_events_publish_apex.htm
4: https://developer.salesforce.com/docs/atlas.en-us.platform_events.meta/platform_events/platform_events_define.htm