The divergence between money costs and opportunity costs is the least in which of the following situations?

a. China uses millions of otherwise unemployable workers to build roads with picks and shovels.
b. Wilhelm, an engineer at Exxon, is drafted-his army salary is $2,000 per month.
c. Colleen quits her job to stay at home and raise her children.
d. A university, using a private contractor, builds a field house on land it purchased at full market value from a local farmer.

d