To provide seamless user experience during upgrades or maintenance The primary purpose of maintaining two identical environments in a blue-green deployment is to ensure a seamless user experience during upgrades or maintenance. This approach allows for one environment (blue) to be active while the other (green) is updated or maintained. Users are then switched over to the updated environment with minimal disruption. Option A is incorrect because using one environment for development and the other for production is not the primary goal of blue-green deployment, which focuses on seamless transitions during updates. Option B is incorrect as A/B testing is not the main objective of blue-green deployment, which is more about minimizing downtime and ensuring service continuity. Option D is incorrect because dividing the workload between servers is not the fundamental purpose of this strategy; rather, it's about having a ready-to-go, updated environment.