Question $7(1$ point$)$

What is the most appropriate precondition that should be included in the docstring for this function:

def slope $(x1,x2,y1,y2)$ :

return $\frac{y2-y1}{x2-x1}$

Precondition: $x2-x1>0$ and $y2-y1>0$

Precondition: $21$

$($where the $!=$operator means "not equal to$")$

No precondition is needed.

Precondition: $x2>x1$