You have an application running in us-west-2 that requires 6 EC2 instances running at all times. With 3 AZ available in that region, which of the following deployments provides 100% fault tolerance if any single AZ in us-west-2 becomes unavailable. Choose 2 answers from the options below

Answer options:

A.us-west-2a with 2 instances, us-west-2b with 2 instances, us-west-2c with 2 instances
B.us-west-2a with 3 instances, us-west-2b with 3 instances, us-west-2c with 0 instances
C.us-west-2a with 4 instances, us-west-2b with 2 instances, us-west-2c with 2 instances
D.us-west-2a with 6 instances, us-west-2b with 6 instances, us-west-2c with 0 instances
E.us-west-2a with 3 instances, us-west-2b with 3 instances, us-west-2c with 3 instances

Answer - D and E
Since we need 6 instances running at all times, only D and E fulfil this option.
The AWS documentation mentions the following on Availability zones
When you launch an instance, you can select an Availability Zone or let us choose one for you. If you distribute your instances across multiple Availability Zones and one instance fails, you can design your application so that an instance in another Availability Zone can handle requests.
For more information on Regions and AZ’s please visit the URL:
http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/using-regions-availability-zones.html