Diminishing Marginal Returns Occurs When

Diminishing marginal returns occurs when

A) each additional unit of a variable factor adds less to total output than the previous unit, given constant quantities of other factors.
B) each additional unit of a variable factor adds more to total output than the previous unit, given constant quantities of other factors.
C) each additional unit of a variable factor diminishes total output, given constant quantities of other factors.
D) each additional unit of a variable factor adds a constant amount to total output than the previous unit, given diminishing quantities of other factors.