An organization wants to deploy a two-tier web application on AWS.

Hello.
If you are familiar with working with serverless architectures, you could use AWS Amplify, Lambda, S3, etc. for the front and back ends.
By using serverless services, the infrastructure, such as the OS, is managed by AWS, and we, the users, can use the service without being aware of availability.
https://aws.amazon.com/jp/blogs/compute/lifting-and-shifting-a-web-application-to-aws-serverless-part-1/

If they want to manage their own operating systems, etc. as in traditional on-premises, they would use EC2.
It is possible to manage EC2 with AutoScaling, etc., and achieve high availability.
https://aws.amazon.com/ec2/autoscaling/?nc1=h_ls

There are different ways to select a database, but if you choose a relational database, use RDS.
This one can be multi-AZ by setting it up.
High availability can be achieved by performing multi-AZ configuration.
https://aws.amazon.com/rds/features/multi-az/?nc1=h_ls

https://www.projectpro.io/article/top-50-aws-interview-questions-and-answers-for-2018/399

7. An organization wants to deploy a two-tier web application on AWS. The application requires complex query processing and table joins. However, the company has limited resources and requires high availability. Which is the best configuration for the company based on the requirements?

DynamoDB deals with core problems of database storage, scalability, management, reliability, and performance but does not have an RDBMS’s functionalities. DynamoDB does not support complex joins or query processing, or complex transactions. You can run a relational engine on Amazon RDS or Amazon EC2 for this kind of functionality.