(exercise on p.70)
I recently wrote an e-mail to a fellow student advocating a boating program we had both participated in and lamenting the lack of students this year.  I made clear that we needed more people and that the person was welcome.  I also responded to the person's reason for not taking the class (she didn't have the class time totally free) by pointing out that it is a flexible program that would welcome her at whatever times she could join us.