The Marginal Rate of Technical Substitution May Be Defined as All

The marginal rate of technical substitution may be defined as all of the following except:

A) the rate at which one input may be substituted for another input in the production process,while total output remains constant
B) equal to the negative slope of the isoquant at any point on the isoquant
C) the rate at which all combinations of inputs have equal total costs
D) equal to the ratio of the marginal products of X and Y
E) b and c