Indicate whether each of the following statements is true, false, or uncertain, and justify your answer.

a. Efficient provision of a public good occurs at the level at which each member of society places the same value on the last unit.

b. If a good is nonrival and excludable, it will never be produced by the private sector.

c. A road is nonrival because one person's use of it does not reduce another person's use of it.

d. Larger communities tend to consume greater quantities of a nonrival good than smaller communities.