Which of the Following Best Explains the Concept of 'External

Which of the following best explains the concept of 'external structure'? 

A)  A series of companies (links) in which the consecutive stages of production of an economic product take place, from primary producer to final consumer. 
B)  A number of links (companies) that are connected via markets. 
C)  The horizontal relationship of organizations that experience each other as effective competitors. 
D)  A sub-division of an organization.