When a Production Function Exhibits a Diminishing, but Positive, Marginal

When a production function exhibits a diminishing, but positive, marginal product of labor,

A) output increases, but at an increasing rate, as more workers are employed.
B) output increases, but at a decreasing rate, as more workers are employed.
C) output declines as more workers are employed.
D) the effects on marginal product are ambiguous.