What is the difference between a line organization and a line$-$and$-$staff organization?

a$.$ A line$-$and$-$staff structure has staff specialists who perform specific services or act as management advisers in particular areas.

b$.$ Line organizations are used in large firms, whereas most very small firms use a line$-$and$-$staff organization.

c$.$ In a line$-$and$-$staff organization, each person may report to more than one supervisor.

d$.$ The span of control in a line organization is larger than the span of control in a line$-$and$-$staff organization.