The correct answer is B because independent applications should have independent Terraform root configurations and state boundaries. Google Cloud Terraform best practices state that to manage applications and projects independently, resources for each application and project should be placed in their own Terraform directories. This avoids a single oversized root module and reduces coupling between unrelated applications. Grouping by resource type creates artificial coupling because one application change can affect the same shared state as other applications. Putting all modules in one directory does not establish independent root configurations. A root directory per application gives clearer ownership, safer deployments, and better separation of lifecycle, state, and permissions.

Cloud Functions is Google Cloud's event-driven serverless compute platform that lets you run your code locally or in the cloud without having to provision servers. Cloud Functions scales up or down, so you pay only for compute resources you use. Cloud Functions have excellent integration with Cloud Pub/Sub, lets you scale down to zero and is recommended by Google as the ideal serverless platform to use when dependent on Cloud Pub/Sub.
"If you're building a simple API (a small set of functions to be accessed via HTTP or Cloud Pub/Sub), we recommend using Cloud Functions." Ref: https://cloud.google.com/serverless-options

When you intially click on Monitoring(Stackdriver Monitoring) it creates a workspac(a stackdriver account) linked to the ACTIVE(CURRENT) Project from which it was clicked.
Now if you change the project and again click onto Monitoring it would create an another workspace(a stackdriver account) linked to the changed ACTIVE(CURRENT) Project, we don't want this as this would not consolidate our result into a single dashboard(workspace/stackdriver account).
If you have accidently created two diff workspaces merge them under Monitoring > Settings > Merge Workspaces > MERGE.
If we have only one workspace and two projects we can simply add other GCP Project under Monitoring > Settings > GCP Projects > Add GCP Projects.
https://cloud.google.com/monitoring/settings/multiple-projects
Nothing about groups https://cloud.google.com/monitoring/settings?hl=en

The goal is to pull (fetch) messages from a subscription and acknowledge them.
* The gcloud pubsub subscriptions **pull** command retrieves messages from a specified subscription.
* The --auto-ack flag instructs the command to automatically acknowledge the messages after they are successfully retrieved, combining the two required actions into one command.
Reference: Google Cloud Documentation - gcloud pubsub subscriptions pull:
"Pulls one or more messages from the specified subscription. To acknowledge the pulled messages, use the -- auto-ack flag."

https://cloud.google.com/spanner/docs/getting-started/set-up