As a Performance Measure for Social Networks, the Interaction Rate

As a performance measure for social networks, the interaction rate is

A) the total number of people who are fans of the post divided by the total number of people in the target demographic.
B) the number of people who "like" a post.
C) the number of people who read a post on a page divided by the total number of people seeing the post.
D) the number of people who connect with a post divided by the total number of people seeing the post.
E) the number of people who visit the product website and click on at least one link.