Option A is not ideal as it involves assigning public IP addresses to servers, contradicting security requirements. Moreover, relying solely on IP addresses for Google services is unreliable due to potential changes. Option B introduces unnecessary complexity by setting up a proxy server in Compute Engine, which is not required for accessing Cloud Storage. Option C suggests migrating servers to Compute Engine and using an ILB, which is overly complex for the task at hand. Option D is the correct approach, leveraging Private Google Access for on-premises hosts. This method securely connects on-premises systems to Google APIs and services through a Cloud VPN or Interconnect tunnel, without exposing them to the internet. It involves configuring DNS to resolve *.googleapis.com to restricted.googleapis.com, ensuring secure and controlled access to Cloud Storage. This solution aligns with security best practices and requirements. For more details, visit: Private Google Access for on-premises hosts.