Leslie Higgins is trying to schedule projects for his consulting company over the next month. He would like to use an optimization model to help determine which projects to schedule. Suppose that the decision variables are x1, x2 and x3 for this optimization model.

Let x1 = 1 if Leslie chooses to do project 1, and 0 if he chooses NOT to do project 1. Let x2 = 1 if Leslie chooses to do project 2, and 0 if he chooses NOT to do project 2. Let x3 = 1 if Leslie chooses to do project 3, and 0 if he chooses NOT to do project 3.

If Leslie chooses to do project 1, then he MUST also choose to do projects 2 and 3. If Leslie chooses not to do project 1, then there is no requirement on whether or not he chooses to do projects 2 and 3. Which of the following will achieve this logic?

Multiple choice:

A) x1 <= x2 - x3

B) Requires 2 constraints: x1 <= x2 AND x1 <= x3

C) x1 <= x2 + x3

D) x1 + x2 + x3 = 1