A Shopping Complex Is Considering Building a Self-Service Vending Machine $\mathrm{X} 1$

A shopping complex is considering building a self-service vending machine island. The mall can buy a vending machine for dispensing various types of ready-to-pop corn. Purchase of this machine is captured by variable $\mathrm{X} 1$ , taking a value of 1 and 0 if not purchased. There is also a machine available for popping any type of corn vended by the vending machine. Purchase of this machine is captured by variable X2, taking a value of 1 and 0 if not purchased. Assume that buying just one of these machines does not do much good. That is, either the mall should buy both or buy neither. The constraint that implements this will be

A) $\mathrm{X}_{1}-\mathrm{X}_{2}<$ 0
B) $\mathrm{X}_{1}-\mathrm{X}_{2} \leq$ 0
C) $\mathrm{X}_{1}-\mathrm{X}_{2} \geq$ 0
D) $X_{1}-X_{2}=$ 0
E) $X_{1}-X_{2}>$