Which of the following best describes the short run?

The concept of the short run in economics is defined by the presence of fixed inputs, meaning that at least one factor of production cannot be changed. This is in contrast to the long run, where all inputs can be adjusted freely. In the short run, firms can only modify variable inputs, such as labor or raw materials, while some inputs, like capital equipment or land, remain constant. This restriction affects production capacity and decisions firms make in the short term.

Understanding this distinction is crucial because it impacts how firms respond to changes in demand or costs. For instance, if a sudden increase in demand occurs, a firm in the short run cannot immediately expand its physical plant size but can hire more workers or increase hours for existing employees. This limitation defines the operational constraints that firms face.

Consequently, the other options do not accurately capture the essence of the short run: all inputs cannot be adjusted, costs are always a factor in production decisions, and while investment can affect output in the long run, it does not guarantee increased output in the immediate term.