How can you best resolve the issue of the application responses not meeting your SLA?

You have a web-style application with a stateless but CPU and memory-intensive web tier running

on a cc2 8xlarge EC2 instance inside of a VPC The instance when under load is having problems
returning requests within the SLA as defined by your business The application maintains its state
in a DynamoDB table, but the data tier is properly provisioned and responses are consistently fast.
How can you best resolve the issue of the application responses not meeting your SLA?

A.
Add another cc2 8xlarge application instance, and put both behind an Elastic Load Balancer

B.
Move the cc2 8xlarge to the same Availability Zone as the DynamoDB table

C.
Cache the database responses in ElastiCache for more rapid access

D.
Move the database from DynamoDB to RDS MySQL in scale-out read-replica configuration

Explanation:
http://aws.amazon.com/elasticmapreduce/faqs/