Choice "A" is correct. Segregation of incompatible duties serves to prevent and detect errors or irregularities.
Choice "b" is incorrect. Within the IT department, the duties of system analysts, computer programmers, computer operators, and security administrators should be kept separate to the most practical degree.
Choice "d" is incorrect. Segregation of duties is defined as dividing responsibilities for different portions of a transaction (authorization, recording, and custody) among several different people or departments.
Choice "c" is incorrect. The objective of segregation of duties is to prevent any one person from having total control over all aspects of the transaction.