A Retail Outlet Wants to Replace a Broken Ice Cream $X_{1}$

Multiple Choice

A retail outlet wants to replace a broken ice cream vending machine with one of two models. Purchase of model 1 machine is captured by variable $X_{1}$ taking a value of 1 and 0 if not purchased. $X_{2}$ is similarly defined. They would also want to allow for the possibility of getting rid of the old machine with no replacement. One of the constraints for this problem would be

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