1. Improvements in technology.
2. Increases in the supply (stock) of capital goods.
3. Purchases of expanding output.
4. Obtaining the optimal combination of goods, each at least-cost production.
5. Increases in the quantity and quality of natural resources.
6. Increases in the quantity and quality of Human Resources.

Use the accompanying list to answer the following questions. As distinct from the supply factors and demand factor of economic growth, the efficiency factor(s) of economic growth is (are)

a. 1 only

b. 4 only

c. 1 and 3 only

d. 3 only