Add rules file to a workflow in Visual Studio

I'm trying to create new workflow in Visual Studio, but, I'm using components of Dynamic Workflow from Microsoft (Solution Starters package). I'm trying to add its entire ApprovalActivity section with its rule file. But, the problem is, ApprovalActivity.rules is not recognized as part of this workflow. This is how it looks in my project:

http://postimage.org/image/5uyfazehl/

And this is how it should look like:

http://postimage.org/image/3zuug4m01/

Rules aren't bind with ApprovalActivity.cs.

How can I connect *.rules file with activity?