Consider a capital budgeting formulation where the binary variables \(x_{1}\) and \(x_{2}\) are used to represent the acceptance \(\left(x_{i}=1\right)\) or rejection \(\left(x_{i}=0\right)\) of each alternative. The requirement that \(x_{2}\) is contingent upon \(x_{1}\) can be represented by which of the following?

a. \(x_{1}+x_{2}<=1\)

b. \(x_{2}<=x_{1}\)

c. \(x_{1}+x_{2}>=1\)

d. \(x_{1}<=x_{2}\)