Concept:Demand for labour is a derived demand.
It changes when the demand for the product that labour produces changes.
Explanation:When the demand for output increases, firms need more workers to increase production.
This shifts the labour demand curve to the right.
Among the options, this is the case of “labour’s demand for output,” meaning the demand for the product labour produces.
Increasing the wage rate (A) makes labour more costly, so it reduces the quantity of labour demanded.
A low wage rate (C) moves the employer along the existing demand curve.
It raises the quantity demanded but does not increase demand itself.
Low marginal productivity (D) lowers the contribution of each worker, so it reduces the demand for labour.
Therefore, the correct choice is B.
Answer:B. Labour's demand for output.