1. The source and sink of a maximum flow problem have conservation of flow constraints. True or False?

2. A nonlinear function may contain a product of two variables. True or False?

3. In a binary integer problem with 2 mutually exclusive alternatives, X1 and X2, the following constraint needs to be added to the formulation if one alternative must be chosen:

A. X1 + X2 <= 1

B. X1 + X2 = 1

C. X1 - X2 <= 1

D. X1 - X2 = 1

E. None of the above