When Hallmark designs its website so that a teenage girl can send a theme card to her boyfriend's cell phone, what is the primary segmenting dimension that Hallmark is using?

Hallmark is using the Age segmenting dimension.

Explanation:

Most businesses and organizations tend to understand their customers, that is, their behaviors on purchases.

There are 7 important ways businesses segment their customers. They are:

Income Age Gender Acquisition Path First purchase Geography Device type

In our scenario, Hallmark is using the Age segmenting dimension because they can identify that its a teenage girl that is sending theme card to her boyfriend's cell phone.