We need to ensure the global capacity remains intact, for that reason we need to establish maxUnavailable to 0. On the other hand, we need to ensure new instances can be created. We do that by establishing the maxSurge to 1.
Option C is more expensive and more difficult to set up and option D won't meet requirements since it won't keep global capacity intact.
https://cloud.google.com/compute/docs/instance-groups/rolling-out-updates-to-managed- instance-groups#options

Explanation/Reference: https://cloud.google.com/sdk/gcloud/reference/deployment-manager/deployments/update

https://cloud.google.com/sdk/gcloud
If you'd like to work with multiple projects or authorization accounts, you can set up multiple configurations with gcloud config configurations create and switch among them accordingly.
Within these configurations, you can customize properties. For example, to set your project within an active configuration use the project property: gcloud config set project <project-id> Multiple projects require multiple configurations
https://cloud.google.com/sdk/docs/configurations

Reference:
https://cloud.google.com/storage/docs/audit-logs