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
SQL injection is a common application layer attack that targets the database of a web application. SQL injection exploits a security vulnerability in the application's software, such as incorrect filtering of user input, that allows an attacker to send malicious SQL statements to the database. These statements can then be executed to steal, modify, or delete data, or even execute commands on the server1. SQL injection can also bypass authentication and authorization mechanisms, and sometimes even impersonate or damage the underlying system2. SQL injection is one of the most common and dangerous web attacks, and it can cause serious damage to the confidentiality, integrity, and availability of web applications3. References: 1: SQL Injection - OWASP2: SQL Injection - Web Application Firewall - Alibaba Cloud Documentation Center3: Web Application Firewall:What is WAF? - Alibaba Cloud.