You Will Have Several Applications Running on Different Compute Engine

You will have several applications running on different Compute Engine instances in the same project. You want to specify at a more granular level the service account each instance uses when calling Google Cloud APIs. What should you do?

A) When creating the instances, specify a Service Account for each instance.
B) When creating the instances, assign the name of each Service Account as instance metadata.
C) After starting the instances, use gcloud compute instances update to specify a Service Account for each instance. After starting the instances, use gcloud compute instances update to specify a Service Account for each instance.
D) After starting the instances, use gcloud compute instances update to assign the name of the relevant Service Account as instance metadata. to assign the name of the relevant Service Account as instance metadata.