You have been asked to select at least $3$ ?out of $7$ ?possible sites for oil exploration. Designate each site as $S_1,S_2,S_3,S_4,S_5,S_6,$ ?and $S_7.$ ?The restrictions are:

Restriction $1.$ ?Evaluating sites $S_1$ ?and $S_3$ ?will prevent you from exploring site $S_7.$ ?Restriction $2.$ ?Evaluating sites $S_2$ ?or $S_4$ ?will prevent you from assessing site $S_5.$ ?Restriction $3.$ ?Of all the sites, at least $3$ ?should be assessed.

Assuming that $S_i$ ?is a binary variable, write the constraint $($ s $)$ ?for the second restriction.

$S_2+S_5+S_4+S_5?2$

$S_2+S_5?1$

$S_2+S_5?1,S_4+S_5?1$

$S_4+S_5?1$