An observer may conclude that the organizational culture of Zappos, an online retailer for shoes and clothing, might be the basis for its competitive advantage. However, reverse social engineering to crack Zappos' code of success might be much more difficult for a company trying to exactly imitate its strategy. Thus, the source of Zappos competitive advantage is said to be .a. non-ambiguous
b. socially complex
c. inexhaustible
d. non-substitutable

b. socially complex

Explanation:

When competitive advantage are based on such the source is said to be "socially complex". That is the ability for a firm to imitate another firm because of its resources and capabilities and this advantage might not yield positively in the long run.

B) socially complex

Explanation:

When something is said to be socially complex, it means that it involves several aspects of human existence or in this case, corporate existence. As humans we deal with different phenomena in our cultures, e.g. immigration, conflicts, political movements, unions between individuals (formerly marriages), etc.

A socially complex organization has a strong and unique organizational culture, well defined and efficient leadership and strong interpersonal relationships between the internal actors (employees and management) and also with external actors (customers and their relationship with the organization).  

That is why Zappo's organizational model is so hard to copy since you cannot replicate an organization's culture, you can only try to imitate it but the results may not necessarily be positive. What works for a society might not work for another, and the same applies to different companies.