Which of the following statements illustrates diminishing returns? a. the second billion hours of labor changes real gdp from $1 to $3 trillion and the third billion hours of labor changes real gdp from $3 to $4 trillion. b. the second billion hours of labor changes real gdp from $1 to $2 trillion and the third billion hours of labor changes real gdp from $2 to $3 trillion. c. the second billion hours of labor changes real gdp from $1 to $2 trillion and the third billion hours of labor changes real gdp from $2 to $4 trillion. d. the second billion hours of labor changes real gdp from $1 to $5 trillion and the third billion hours of labor changes real gdp from $5 to $9 trillion.