Six-year-old kian is in the stage of cognitive development, whereas his 10-year-old brother is likely in the stage.

preoperational; concrete operations                

Explanation:

Jean Piaget has given the theory of cognitive development in which he has mentioned four different stages including sensorimotor, preoperational, concrete operational, and formal operational.

Preoperational stage: This is the second stage in the cognitive development theory and starts from the age of two years and lasts through seven years of age in a child's stage. At this stage, a child is being engaged in manipulating symbols and symbolic play.

Concrete Operational Stage: This stage is the third stage and starts at seven years of age and lasts through eleven years of a child's life. In this stage, a child is engaged in using logical operations or thought and therefore the child can put logic only to physical objects.

saving account is right

marginal cost is a microeconomic measure that us to evaluate the extent to which the level of production of a good is sustainable in accounting, that is, to how many quantities the company plans to profit from the production of the good.

the concept of marginal cost is simple, it means the cost of producing one more item. for example, in the case of pies, the marginal cost is the cost of producing one more pie than those that have already been produced.

it is important to understand that productive activity influences marginal cost. the marginal cost of some goods can be very high, while others may be insignificant. for example, the marginal cost of producing an extra plane is very high. already the marginal cost of a water company to provide 1l more water is derisory.

in the case of pies, the cost involves the inputs, the labor and the fixed cost, which involves the fixed space of the bakery. the level of production initially has the marginal cost decreasing because there is space and manpower available. however, to produce more you have to hire more workers and buy more inputs. if physical space is limited, workers will conflict with places, inputs and their productivity will decrease, meaning there is an optimum point of production for each level of space and manpower. from this point on, the productivity of the workers will be getting smaller because of lack of space, so that the marginal cost of producing one more pie will be increasing. so, although you have not posted the chart, but if you have the answer, you can see that my explanation goes according to the marginal cost curve that will increase from the 4th pie, answer (c).