PCA (Prometheus Certified Associate) sample exam question with answer 263

Question:
What does the following metric_relabel_config do?

scrape_configs:
  - job_name: example
    metric_relabel_configs:
      - source_labels: [datacenter]
        regex: (.*)
        action: replace
        target_label: location
        replacement: dc-$1

1. changes the value of the datacenter label to be prepended with dc
2. Drops all metrics that are not from DC-1
3. Changes the datacenter label to location and prepends the value with dc-
4. removes the datacenter label

Answer:
C - correct answer