Question $3(1$ 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: $x2>x1$

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

No precondition is needed.

Precondition: $x2x1$

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