What Is the Distinction Between Vertical and Horizontal Specialization Within

What is the distinction between vertical and horizontal specialization within rehabilitation counseling?

A) There is no distinction in relation to practice
B) Vertical specialization refers to the elevation of a function to a role, while horizontal specialization covers all the functions, but specializing in a particular client group
C) Vertical specialization is the modern term, whereas horizontal specialization refers to the way practice was conceptualized years ago
D) All of the above are true