What Assumption(s) of the Error Terms in a Least Squares

What assumption(s) of the error terms in a least squares solution of the linear regression model must be satisfied?

A) The mean of the disturbance term must equal one.
B) The variance of the disturbance term is independent of the values of the predictor variable.
C) The values of the error term are independent of one another.
D) all of the above.
E) Both b and c above must be satisfied.