How many types of block devices does Amazon EC2 support?

How many types of block devices does Amazon EC2 support?

A.
2

B.
3

C.
4

D.
1

Explanation:
http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/block-device-mapping-concepts.html Amazon EC2
supports two types of block devices:
Instance store volumes (virtual devices whose underlying hardware is physically attached to the host computer
for the instance)
EBS volumes (remote storage devices)
A block device mapping defines the block devices (instance store volumes and EBS volumes) to attach to an
instance.