Which of the following is the correct definition of the law of diminishing returns? If extra units of one variable input are added to a fixed amount of all other inputs, then sooner or later the marginal returns will get smaller. If extra units of one variable input are added to a fixed amount of all other inputs, then the marginal returns will always get smaller. If extra units of all variable inputs are added to a fixed amount of all fixed inputs, then the marginal returns will always get smaller. If extra units of all variable inputs are added to a fixed amount of all fixed inputs, then sooner or later the marginal returns will get smaller.