Final answer:
Best illustrating increased productivity is a factory doubling the production of shoes from the same amount of leather, as this shows more output from the same input.
Step-by-step explanation:
The situation that best illustrates a business increasing its productivity is C. A factory doubles the number of shoes it can produce from a particular amount of leather. This example clearly shows an increase in productivity since the firm is able to produce more output with the same amount of input, which is a key feature of productivity improvements. The scenario exemplifies an efficient use of resources and likely the adoption of better production technology or methods that allow for a greater yield from the material without increasing labor costs. This approach is particularly relevant when considering economies of scale, where as output increases, the cost per unit typically goes down. In comparison, the other situations do not directly relate to improving the efficiency of the production process itself but rather address quality issues, decrease output, promote products, or react to labor market dynamics.