Using Amazon IAM, can I give permission based on organizational groups?

A.
Yes but only in certain cases

B.
No

C.
Yes always

Explanation:
An IAM group is a collection of IAM users. You can use groups to specify permissions for a collection of users,
which can make those permissions easier to manage for those users.
http://docs.aws.amazon.com/IAM/latest/UserGuide/id.html