Which of the following would cause an increase in economic growth?

a. An increase in the quality of human capital and a decrease in investment spending.

b. A decrease in the quantity of human capital and an increase in capital investment.

c. An increase in the real interest rate and an increase in investment spending.

d. An increase in labor productivity and an increase in capital investment.

e. An increase in spending on education and training and an increase in the real interest rate.