In a BIP Problem with 2 Mutually Exclusive Alternatives,x₁ and X₂,the

In a BIP problem with 2 mutually exclusive alternatives,x₁ and x₂,the following constraint needs to be added to the formulation:

A) x₁ + x₂ $\le$ 1.
B) x₁ + x₂ $\ge$ 1.
C) x₁ - x₂ $\le$ 1.
D) x₁ - x₂ = 1.
E) None of the above.