The correct option is Establish a continuous stream to receive immediate notifications of resource changes.

The Establish a continuous stream to receive immediate notifications of resource changes watch verb lets clients open a long lived connection to the API server so they receive events when resources are added, modified, or deleted. The API server sends discrete event types such as ADDED, MODIFIED, and DELETED and clients can use resourceVersion to resume or continue a watch stream reliably.

Create a new resource instance is incorrect because creating resources uses POST or apply operations and not the watch verb which only observes changes.

Cloud Pub/Sub is incorrect because that is a separate messaging service from Google and it is not a Kubernetes API verb or feature for observing resource changes.

Modify the current state of a resource is incorrect because changing a resource uses update or patch operations and not watch which only reports events about changes.

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