Explanation
When using Alibaba Cloud SLB, users can enable the health check function to monitor the availability of the backend ECS instances. If a backend ECS instance A is running abnormally, SLB will stop forwarding requests to it and distribute them to other healthy ECS instances. This way, SLB can ensure the high availability and reliability of the service. When the backend ECS instance A is back to normal, SLB will resume forwarding requests to it. SLB performs health checks on the backend ECS instances at regular intervals and updates their status accordingly. Users can configure the health check parameters such as the protocol, port, interval, timeout, and threshold on the SLB console or by using the API. References: 1 - Health checks - Server Load Balancer - Alibaba Cloud Document Center - Health check overview

Explanation
The transmission acceleration service for OSS is a feature that allows you to access OSS buckets through a global acceleration endpoint, which can improve the upload and download speed of OSS data across regions.
The global acceleration endpoint is a domain name that is resolved to the nearest OSS access point based on the network conditions of the client. This way, the data transmission distance is shortened and the network latency is reduced. Therefore, option C is the correct answer. References: Enable transfer acceleration, Map an acceleration endpoint

Explanation
According to the Alibaba Cloud documentation1, Auto Scaling is a service that automatically adjusts the number of elastic computing resources based on your business demands and policies. When the demand for computing resources increases, Auto Scaling automatically adds ECS instances to ensure sufficient computing capabilities. When the demand decreases, Auto Scaling automatically removes ECS instances to reduce costs.
Auto Scaling supports adding an existing ECS instance into the scaling group, but the instance must meet some requirements1. One of the requirements is that the instance and the scaling group must be in the same region. However, they do not have to be in the same zone. A zone is a physical area within a region that has independent power grids and networks. A region is a geographic area where Alibaba Cloud deploys its resources. Therefore, the correct answer is B.
References:
1: Auto Scaling: Automatically Adjusts Computing Resources - Alibaba Cloud
2: Introduction to Auto Scaling - Alibaba Cloud Document Center