Employing an Additional 1 Billion Hours of Labor Increases Real

Employing an additional 1 billion hours of labor increases real GDP by $12 billion. Employing another 1 billion hours beyond the first 1 billion increases real GDP by $11 billion. Hence we can conclude from this information that as employment increases, real GDP

A) increases at an increasing rate.
B) decreases at an increasing rate.
C) decreases at a decreasing rate.
D) increases at a decreasing rate.
E) falls from $12 billion to $11 trillion as more workers are hired.