Answer: Option D
Explanation: Mary Parker believed that management is the art of making people do things you want. To achieve this both senior and subordinates should work in collaboration.
In the given case, the employees in the organisation are starting cliques, that is they are not accepting the outsiders and are not communicating with them. Thus, if the employees develop an attitude that they are a community then they could collaborate with each other.
Hence from the above we can conclude that the correct option is D.