If Adding an Initial 100 Billion Labor Hours Per Year

If adding an initial 100 billion labor hours per year increases real GDP by $3 trillion,diminishing returns informs us that an additional 100 billion labor hours per year will increase real GDP by

A) exactly $3 trillion.
B) less than $3 trillion.
C) more than $3 trillion.
D) either exactly $3 trillion or by less than $3 trillion,depending on whether the real wage rate remains constant or rises.
E) some amount but there is not enough information to tell by how much.