Sue and Mark Are the Only Two Members of a Community

Multiple Choice

Sue and Mark are the only two members of a community. Sue's marginal benefit from one lighthouse is $2,000 and Mark's marginal benefit is $1,000. If the marginal cost of one lighthouse is $2,500 and if a lighthouse is a public good, then for efficiency the lighthouse should

A) be built, but only Sue should be allowed to use it.
B) be built, but only Mark should be allowed to use it.
C) not be built because its marginal cost exceeds Sue's marginal benefit.
D) not be built because its marginal cost exceeds both Sue's and Mark's marginal benefit.
E) be built and both Sue and Mark should be allowed to use it.