How would you write down a univariate regression model in which company output, $Y,$ depends on a

single input $x$ and an error term, $u?$

Select one:

$Y=a+u$

$x=a+cY+dxZ+u$

$x=a+bxY+u$

$Y=a+bx+u$

$x=a+cxY+u$