Concept:In the short-run, one or more factors of production are fixed, so a firm can raise output only by using more variable inputs.
Explanation:The short-run is a period in which at least one factor, such as capital or machinery, cannot be changed.
Therefore, the firm cannot increase output by buying new machines or expanding equipment.
It can increase output by employing more of the variable inputs, such as raw materials or labour.
Among the given choices, increasing raw materials is a variable input change that can be done quickly in the short-run.
So, the correct option is D.
Answer:D. increasing the quantity of raw materials.