Manage sudden spikes in traffic, minimize response time and maintain 99.99% availability of your web application with Server Load Balancer.
Reference:
https://arcelon.co.id/product/server_load_balancer.php

Explanation
A is the correct answer because Auto Scaling supports adding existing ECS instances into the scaling group, whose status however must be running. Running means that the ECS instance is in a normal state and can provide services. Auto Scaling does not support adding ECS instances that are in other states, such as created, stopped, or preparing. Created means that the ECS instance has been created but has not been started yet.
Stopped means that the ECS instance has been stopped and cannot provide services. Preparing means that the ECS instance is being initialized and cannot provide services12 B, C, and D are incorrect answers because they are not valid states for adding existing ECS instances into the scaling group.
References: 1: Add existing ECS instances to a scaling group 2: ECS instance lifecycle

Explanation
Alibaba Cloud relational database service (RDS) is a stable, reliable and elastic online database service that supports various database engines, such as MySQL, SQL Server, PostgreSQL, MariaDB, and PPAS (PostgreSQL with Oracle compatibility)1. RDS provides high availability, backup and recovery, security, and monitoring features for your databases. RDS does not support Oracle database, which is a proprietary database system developed by Oracle Corporation2. If you need to use Oracle database on Alibaba Cloud, you can deploy it on an ECS instance or use the Oracle Database Backup Service3.
References: 1: Alibaba Cloud Academy, "RDS Concepts",
https://edu.alibabacloud.com/elearning/lesson/ACA-Cloud-Computing-Certification/lesson-5-rds-concepts 2:
Oracle, "Oracle Database", https://www.oracle.com/database/ 3: Alibaba Cloud, "Oracle Database Backup Service", https://www.alibabacloud.com/product/oracle-database-backup-service

Explanation
Server Load Balancer (SLB) can help protect from distributed denial-of-service (DDoS) attacks by distributing network traffic across groups of backend servers to improve the service capability and application availability. SLB also supports built-in Anti-DDoS services to ensure business security. Anti-DDoS services can mitigate DDoS attacks at the Tbit/s level and provide multiple defense methods, such as blackhole filtering, traffic scrubbing, and access control1. In addition, you can integrate Application Load Balancer (ALB) with Web Application Firewall (WAF) in the console to ensure security at the application layer and prevent attacks such as SQL injection2. References: 1: Server Load Balancer(SLB) - Alibaba Cloud2: Associate an EIP protected by Anti-DDoS Pro/Premium with an ALB instance - Server Load Balancer - Alibaba Cloud Documentation Center.