Explanation

Amazon Lex triggers backend processing by invoking AWS Lambda functions. Here's how it works:

• AWS Lambda Integration: When Lex gathers all required slot values and is ready to fulfill an intent (like "book appointment"), it invokes a Lambda function to process the request.

• Functionality: The Lambda function contains the business logic to handle the action, such as making database calls, processing data, or integrating with other services.

• Response Handling: The Lambda function returns a response to Lex, which then sends the appropriate message back to the user.

Why other options are incorrect:

• B) S3: S3 is for storage, not for triggering backend processing
• C) SNS: SNS is for pub/sub messaging, not the primary method for Lex backend processing
• D) EC2: EC2 instances are for compute, but Lex doesn't launch instances for backend processing

This Lambda integration allows Lex to execute complex backend operations while maintaining the conversational flow with users.