When the black hole policy is triggered by excessive DDoS traffic, the affected server is temporarily isolated from the network to prevent further damage. During this period, no services are available, meaning the server cannot provide limited-speed services.

When using Auto Scaling with Server Load Balancer (SLB), both the scaling group and the SLB instance must reside in the same region. This is because region-specific configurations enable low-latency connections and proper integration between the resources, ensuring the scaling group can register with the SLB instance effectively.

Explanation
Changing an instance's operating system requires creating a custom image or using a public image, and then replacing the system disk of the instance. This process will cause the instance to restart. Therefore, this statement is false. References: ECS User Guide: Replace the system disk (non-public image) and ECS User Guide: Replace the system disk (public image)

According to the Alibaba Cloud Academy, a VPC is an isolated network environment that is completely isolated from each other. Each VPC has an independent tunnel ID, and a tunnel ID corresponds to a virtualized network. This means that different VPCs cannot communicate with each other through the tunnel ID. Subnets are not divided like the traditional network environment, but rather are logical divisions of the VPC. Different cloud servers within each subnet are connected by the same router, but different subnets are interconnected by route tables, not switches. ECS instances in a VPC use security group firewalls for Layer 4 network access control, not Layer 2. The internal networks of different VPCs are completely isolated and can be interconnected through IP addresses mapped to the outside, such as NAT Gateway or EIP. References:
ACP Cloud Computing Certification Preparation Course - Internetworking with VPC, Alibaba Cloud VPC User Guide