The Graph Below Illustrates the Concept of a Production Function

The graph below illustrates the concept of a production function and diminishing returns, where an increase in k results in a:

A) large increase in real GDP per worker in area 1.
B) small increase in real GDP per worker in area 1.
C) large increase in real GDP per worker in area 2.
D) small increase in real GDP per worker in both area 1 and area 2.