麻烦老师解释一下这里diminishing marginal productivity does not occur

问题如下：

Based on the Cobb–Douglas production function, diminishing marginal productivity does not occur when:

选项：

A.only labor input is increased B.only capital is increased. C.both labor input and capital input are increased proportionally.

解释：

A Incorrect because the exponents on the K (quantity of labor) and L (estimate of the capital services provided by the stock of equipment and structures used to produce goods and services) variables in the Cobb–Douglas production function sum to one, indicating constant returns to scale—that is, there are no diminishing marginal returns if both inputs are increased proportionately.

B Incorrect because the exponents on the K (quantity of labor) and L (estimate of the capital services provided by the stock of equipment and structures used to produce goods and services) variables in the Cobb–Douglas production function sum to one, indicating constant returns to scale—that is, there are no diminishing marginal returns if both inputs are increased proportionately.

C Correct because the exponents on the K (quantity of labor) and L (estimate of the capital services provided by the stock of equipment and structures used to produce goods and services) variables in the Cobb–Douglas production function sum to one, indicating constant returns to scale—that is, there are no diminishing marginal returns if both inputs are increased proportionately.