A. 1. Create a service account.
2. Give the Cloud Run Invoker role to that service account for your Cloud Run application.
3. Create a Cloud Pub/Sub subscription that uses that service account and uses your Cloud Run application as the push endpoint.

B. 1. Grant the Pub/Sub Subscriber role to the service account used by Cloud Run.
2. Create a Cloud Pub/Sub subscription for that topic.
3. Make your application pull messages from that subscription.

C. 1. Create a Cloud Function that uses a Cloud Pub/Sub trigger on that topic.
2. Call your application on Cloud Run from the Cloud Function for every message.

D. 1. Deploy your application on Cloud Run on GKE with the connectivity set to Internal.
2. Create a Cloud Pub/Sub subscription for that topic.
3. In the same Google Kubernetes Engine cluster as your application, deploy a container that takes the messages and sends them to your application.