Answer:
In three stages of production to which are hold by the law of diminishing marginal returns the second stage is considered to as the rational stage of production as compared to the first and third stage this is due to the fact that this stage it comes out with the best assumptions for efficient and sustainable production, thereby the stage it simultaneously shows the positivity of the average products and marginal product hence, in the increase of labour the total production or outputs increased likewise with the same quantity of fixed factor, therefore this stage it gives direction to the producer on how the higher units of output can be produced.
Unlike the first stage to which it shows each additional variable could enhance more production and such this it signifies an increasing of marginal return but for this case it do not give out the direction in permanent production since labours are needed fewer and in the decrease in number of labour can brings about underproduction.
Also the third stage marginal return is frankly negative because in adding more variable inputs will further led into adding more number of labour hence the increase of labour will contributes to under production as it may be due to labour capacity and efficiency concern.