$21$ and $202$ are binary variables representing whether or not candidate $1$ or candidate $2$ is hired represents hiring candidate $1$;$x_2=1$ represents hiring candidate $2).$ Which of the following constraints correctly specifies the logic that at most one of these two candidates should be hired?

$2x+28=1$

$x_1+2x1$

$23+281$

$E_1=1$;$E_2=0$