What Is the Primary Difference Between Formal and Informal Professional

What is the primary difference between formal and informal professional networks?

A) Formal networks are maintained via face-to-face conversations, whereas informal networks are maintained over email.
B) Formal networks are based on strict reporting structures, whereas informal networks consist of voluntary professional connections.
C) Formal professional networks are made up of managers and more senior employees, whereas informal networks are reserved for lower-level employees.
D) Formal professional networks require membership fees, whereas informal networks are free.
E) Formal networks are encouraged by employers, whereas informal networks are discouraged.