Which of the following is not true about the law of diminishing returns? It is a short run phenomenon. It refers to diminishing marginal product. It will have an impact on the firm's marginal cost. It divides Stage I and II of the production process. All of the above are true.

All of the above are true.

Explanation:

The law of diminishing returns was first formulated by the classic economist David Ricardo. It presupposes a technical relationship between input and output, which is not scientifically demonstrable but only empirically. In practice, in a generic production system, at any contribution of any factor, that is, land, labor, capital, machines, etc. there is no proportionally increasing production increase.

Normally it is assumed that the law does not always come into operation but only when the variable input exceeds a certain threshold. For example, the increase of workers on an assembly line certainly allows a proportional increase in production, but only until the entire system begins to suffer from malfunctions due to logistics or work organization, precisely because of the its getting bigger. Large industrial plants have shown that they must be divided into sections, however coordinated, precisely because of the decreasing returns. This is because the increase in the number of workers and the mass of the plants does not correspond to a consequent increase in production.