title: How to enable Cloud Pub/Sub API to use it in App Engine
body: <p>You want to send and consume Cloud Pub/Sub messages from your App Engine application. The Cloud Pub/Sub API is currently disabled. You will use a service account to authenticate your application to the API. You want to make sure your application can use Cloud Pub/Sub. What should
  you do?</p>
  
  <p>A. Enable the Cloud Pub/Sub API in the API Library on the GCP Console.</p>
  
  <p>B. Rely on the automatic enablement of the Cloud Pub/Sub API when the Service Account accesses it.</p>
  
  <p>C. Use Deployment Manager to deploy your application. Rely on the automatic enablement of all APIs used by the application being deployed.</p>
  
  <p>D. Grant the App Engine Default service account the role of Cloud Pub/Sub Admin. Have your application enable the API on the first connection to Cloud Pub/Sub.</p>
  
  <p>I realized that if I build an app that uses pubsub. it works without manually enabled the pubsub api. But I couldn't find anything in the documentation about that. Which is the correct answer?</p>