Option D is not the best solution because it involves configuring the permissions on the main account's EventBridge event bus to receive events from all accounts, which can lead to potential security risks. Allowing other AWS accounts to send events to the main account's EventBridge event bus can potentially open up a security vulnerability, as it increases the attack surface area for the main account.
On the other hand, option A is the best solution because it involves using Amazon EventBridge, which is a serverless event bus that can be used to route events between AWS services or AWS accounts. By configuring Amazon EC2 to deliver the EC2 instance lifecycle events from all accounts to the Amazon EventBridge event bus of the main account, and adding the SQS queue as a target of the rule, the application can collect all the lifecycle events of the EC2 instances in a single queue in the main account without compromising the security posture of the AWS environment.