A firm has prepared the following binary integer program to evaluate a number of potential locations for new warehouses. The firm's goal is to maximize the net present value of their decision while not spending more than their currently available capital.

Max $20x_1+30x_2+10x_3+15x_4$

$s.t.5x_1+7x_2+12x_3+11x_{4}21\{$ Constraint $1\}$

$x_1+x_2+x_3+x_{4}2\{$ Constraint $2\}$

$x_1+x_{2}1\{$ Constraint $3\}$

$x_1+x_{3}1\{$ Constraint $4\}$

$x_2=x_4\{$ Constraint $5\}$

$x_j=\{\begin{array}{ccc}1,& if\text{l}\text{o}\text{a}\text{c}\text{t}\text{i}\text{o}\text{n}jis\text{s}\text{e}\text{l}\text{e}\text{c}\text{t}\text{e}\text{d}& \end{array}$

$0,$ otherwise

Which of the constraints ensures that at least two of the potential sites will be selected?

Constraint $4$

Constraint $1$

Constraint $5$

Constraint $3$

Constraint $2$