Why Is There Often Disagreement Amongst Economists

Why is there often disagreement amongst economists?

A) Some who claim to be economists may not be sufficiently well trained.
B) There is disagreement over what is, and what is not, a legitimate goal for society to try to achieve, possibly because some economists are 'left wing' and others are 'right wing.'
C) The discipline is so wide and complex that no one person could be expected to cover the whole range of possible knowledge.
D) There is truth in all of the above