What Is the Concept Behind Separation of Duties in Establishing

What is the concept behind separation of duties in establishing internal controls?

A) The company's financial accountant should not share information with the company's tax accountant.
B) Duties of middle-level managers should be clearly separated from those of top executives.
C) Employee fraud is less likely to occur when access to assets and access to accounting records are separated.
D) The external auditors of the company should have no contact with managers while the audit is taking place.