See that info :

https://aws.amazon.com/professional-services/?nc1=h_ls

"The AWS Professional Services organization is a global team of experts that can help you realize your desired business outcomes when using the AWS Cloud. We work together with your team and your chosen member of the AWS Partner Network (APN) to execute your enterprise cloud computing initiatives."

C & D are correct answers.

C is correct.

Support Concierge - the Concierge Team are AWS billing and account experts that specialize in working with enterprise accounts.

They will quickly and efficiently assist you with your billing and account inquiries, and work with you to implement billing and account best practices so that you can focus on what matters: running your business.

The Technical Account Manager (TAM) will assist with the technical inquires.

Answer is A.

Elasticity is the ability to grow or shrink infrastructure resources.

Question implies that multiple availability zones are being used by the application, meaning no room for downsizing.

B.

Each Region is a separate geographic area.

Each Region has multiple, isolated locations known as Availability Zones.

Reference:

https://aws.amazon.com/tco-calculator/

The question does not talk specifically about the Master account => So A would NOT be a good choice here.

Answer C would allow for any user you choose to receive the Reserved Instance benefit.

(Here is the key: Reservations have an affinity for the account in which they were purchased.)

Intrusion attempts: Your logs show that one or more AWS-owned IP addresses are used to attempt to log in to your resources.

B is correct.

Reference: https://aws.amazon.com/premiumsupport/knowledge-center/report-aws-abuse/

Reference:

https://aws.amazon.com/cloudfront/faqs/

Supporting points for serverless services:

Lambda, Fargate, S3, EFS, DynamoDB, Aurora, SQS, AppSync, Step Functions, Kinesis, Athena

Reference:

https://subscription.packtpub.com/book/virtualization_and_cloud/9781788293723/3/ch03lvl1sec26/vpc-components