The correct answer is A. marginal productivities.
The marginal rate of technical substitution (MRTS) is the rate at which one input can be substituted for another while maintaining a constant level of output. It is measured as the ratio of the marginal productivities of the two inputs.
For example, if a firm is producing widgets using labor and capital, the MRTS of labor for capital is the amount of capital that can be saved by using one more unit of labor, while keeping the level of output constant.
The MRTS is a key concept in economics, as it is used to determine the optimal combination of inputs to use in production. It is also used to analyze the effects of changes in input prices on production.
The other options are incorrect because they do not measure the rate at which one input can be substituted for another while maintaining a constant level of output.
A. Marginal productivities are the additional output that is produced when one more unit of an input is used.
B. Marginal utilities are the additional satisfaction that is obtained from consuming one more unit of a good or service.
C. Marginal subsidies are the additional payments that are made to producers for producing a good or service.
D. Factor quantities are the amounts of inputs that are used in production.