Crazy how correct answers are not being provided by this platform which are charging an absolute arm and a leg for this service ;(

Correct answer D

D. Standard Reserved Instances Reserved Instances offer significant cost savings compared to On-Demand Instances, especially for workloads that are expected to run continuously for a long duration, such as a database server for a 1-year project. Standard Reserved Instances provide a discount on the hourly charge for the instance compared to On-Demand pricing, in exchange for committing to a one- or three-year term. Convertible Reserved Instances offer similar savings but provide more flexibility to change the instance type, operating system, or tenancy during the term. However, they may have a slightly higher cost compared to Standard Reserved Instances due to this flexibility.

From the docs: Standard Reserved Instance enables you to modify Availability Zone, scope, networking type, and instance size (within the same instance type) of your Reserved Instance. Convertible Reserved Instance enables you to exchange one or more Convertible Reserved Instances for another Convertible Reserved Instance with a different configuration, including instance family, operating system, and tenancy.

I believe the Convertible Reserved instance is a better option because the key word is "right-sized". If you choose a Standard Reserved instance, you cannot change it and may be paying for more resources than you need. Whereas, with Convertible instances, you can start small and scale up if needed.

https://docs.aws.amazon.com/whitepapers/latest/cost-optimization-reservation-models/standard-vs.-convertible-offering-classes.html

There is no need to modify in the question, so standard reserved instances are the most cost savings. https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/reserved-instances-types.html

I think it is D, because it says right-sized, meaning that most probably the instance will not change and we need more cost effective. Thus, standard Reserved Instances

For an always-up, right-sized database server running for a project that will last 1 year, the pricing model that provides the MOST cost savings is: B. Convertible Reserved Instances Convertible Reserved Instances provide more flexibility to change the attributes of the Reserved Instances during the term, offering potential savings if the requirements change over time.

I think its D. Key word is the MOST cost savings. Standard Reserved Instance will save you more than Convertible.

D. Standard Reserved Instances

Standard Reserved Instances typically provide the highest discount levels.

B. Convertible Reserved Instances Convertible Reserved Instances provide the most cost savings for an always-up, right-sized database server running for a project that will last 1 year. Convertible Reserved Instances offer significant cost savings compared to On-Demand Instances, and they provide flexibility by allowing you to change the instance type if your needs change during the term.