Data Corp. is considering which of 4 different projects to undertake in order to maximize its net present value (NPV). Define X_i as a binary variable that equals 1 project i is undertaken and 0 otherwise, for i = 1, 2, 3, 4. The NPV and required capital (in millions) for each project are listed below. Which of the following represents the constraint stating that project 2 can be undertaken only if project 3 is undertaken? A. X_2 + X_3 lessthanorequalto 1 B. X_2 - X_3 lessthanorequalto 0 C. X_3 - X_2 lessthanorequalto 0 D. X_2 - X_3 lessthanorequalto 1 E. X_3 - X_2 lessthanorequalto 1