Some of the world's fastest-growing nations have economies

whose growth may not be sustainable, critics charge, due to heavy dependence on:
a. foreign industry, which may pick up and move elsewhere any day.
b. heavy industry, in a largely postindustrial economic era.
c. a large number of people living in extreme poverty, who are not well-educated.
d. commodities such as oil and copper, whose prices are subject to fluctuations.

Answer: d