A Is not correct because the Load Balancer will just load balance access to the uploaded image itself, and not create or autoscale VMs based on that image.
B Is not correct because while the App Engine can scale as a proxy, all requests will still end up on the same Compute Engine instance, which needs to scale itself.
C is correct because a managed instance group can use an instance template to scale based on HTTP traffic.
D is not correct because unmanaged instance groups do not offer autoscaling.
https://cloud.google.com/compute/docs/instance-
groups/#managed_instance_groups_and_autoscaling
https://cloud.google.com/compute/docs/images/export-image
https://cloud.google.com/compute/docs/load-balancing/http/adding-a-backend-bucket-to-content- based-load-balancing

How to update instance templates
Instance templates are designed to create instances with identical configurations. So you cannot update an existing instance template or change an instance template after you create it.
If you need to make changes to the configuration, create a new instance template. You can create a template based on an existing instance template, or based on an existing instance. You can also override instance template fields when creating a VM instance from an instance template.
https://cloud.google.com/compute/docs/instance-
templates#:~:text=So%20you%20cannot%20update%20an,based%20on%20an%20existing%20i nstance.

Google Kubernetes Engine supports secret to store sensitive data such as database passwords and is a google recommended practice.
https://cloud.google.com/kubernetes-engine/docs/concepts/secret

Every subnet must have a primary IP address range. You can expand the primary IP address range at any time, even when Google Cloud resources use the subnet; however, you cannot shrink or change a subnet's primary IP address scheme after the subnet has been created. The first two and last two IP addresses of a primary IP address range are reserved by Google Cloud.
https://cloud.google.com/kubernetes-engine/docs/concepts/alias-ips

If the Windows account does not exist, this command will cause the account to be created and the password for that new account will be returned.
https://cloud.google.com/sdk/gcloud/reference/beta/compute/reset-windows-password