39. What is the biggest problem of using government actions such as taxes and emission charges to control external costs?

a.    insufficient legal power to enforce the controls

b.    obtaining enough data to determine how much the tax or emission charge will be

c.    in some situations, there is no known way to control the external costs

d.    political lobbying and voter disagreement

40. Research leading to the discovery of new knowledge has external benefits because

a.    the new knowledge increases profits.

b.    the new knowledge decreases costs.

c.    others can use the new knowledge.

d.    Both answers (a) and (b) are correct.