Which of These Is Not a Reason for Adding a Disturbance

Multiple Choice

Which of these is not a reason for adding a disturbance term to a regression model ?

A) Some determinants of the effect variable may be omitted from the model
B) Some determinants of the effect variable may be unobservable
C) Some determinants of the independent variable may be omitted from the model
D) There may be errors in the way that the dependent variable is measured which cannot be modelled