Which of the Following Statements Concerning Dual Variables Is (Are)

Which of the following statements concerning dual variables is (are) true?

A) Dual variables are obtained automatically in an algebraic solution of a linear programming problem.
B) Dual variables are similar to the artificial variables used in the LaGrange Multiplier technique.
C) A dual variable indicates how much the objective function will change if one additional unit of a given resource is made available, provided that the increase in the resource does not shift the optimal solution to another corner of the feasible solution space.
D) a and c
E) a, b, and c