Amazon RedShift is PB-scale Data Warehouse Service for analyzing structured data.

It is used for 

• for online analytics processing (OLAP) workloads. 
• perform long complex queries on a data warehouse
• run fast, repeat queries and update dashboards

Amazon RDS is a relational (SQL) type of database, not a key-value / nonrelational database. A key-value database is a type of nonrelational (NoSQL) database that uses a simple key-value method to store data.

A key-value database is a type of nonrelational (NoSQL) database that uses a simple key-value method to store data. A key-value database stores data as a collection of key-value pairs in which a key serves as a unique identifier. Amazon DynamoDB is a fully managed NoSQL database service that provides fast and predictable performance with seamless scalability.

It is

• an active-active configuration where reads and writes can take place in multiple regions with full bi-directional synchronization
• key-value database
• No-SQL
• DB you can scale without any downtime
• storing session state data

Amazon ElastiCache is an in-memory caching database. This is not a nonrelational key-value database.

1." highly scalable key-value database" - none of the other options is a key-value database, which is nonrelational (NoSQL).

Enabling volume encryption would not increase resiliency.

You can back up the data on your Amazon EBS volumes to Amazon S3 by taking point-in-time snapshots. Snapshots are incremental backups, which means that only the blocks on the device that have changed after your most recent snapshot are saved. This minimizes the time required to create the snapshot and saves on storage costs by not duplicating data. When you delete a snapshot, only the data unique to that snapshot is removed. Each snapshot contains all of the information that is needed to restore your data (from the moment when the snapshot was taken) to a new EBS volume.

 Instance stores are ephemeral (non-persistent) data stores so would not add any resilience.

Mirroring data would provide resilience however both volumes would need to be mounted to the EC2 instance within the same AZ so you are not getting the redundancy required.

1." backed up durably across multiple Availability Zones" -  so there are only two options that can help with backup durably, i.e mirroring data & regular snapshots. However, mirroring data doesn't have the privilege of being backed on multiple AZs, leave you with the option of regular snapshots.

Standard retrievals

• access your archives within several hours (typically complete within 3–5 hours).
• Default option for retrieval requests

Expedited retrievals

• Quickly access your data when occasional urgent requests for a subset of archives are required.
• Made available within 1–5 minutes.
• Provisioned Capacity ensures that retrieval capacity for Expedited retrievals is available when you need it.

Vault Lock allows you to easily deploy and enforce compliance controls on individual Glacier vaults via a lockable policy (Vault Lock policy).

Bulk retrievals

• S3 Glacier’s lowest-cost retrieval option
• Used to retrieve large amounts, even petabytes, of data inexpensively in a day.
• Complete within 5–12 hours.

1. "delivered within 10 minutes of a retrieval request." only suitable option among the above to get retrieval data within 10 minutes.