As presented in this chapter, as the ${20}^{th}$ century began:

a$.$ Cities were beginning to have electricity.

b$.$ Investments in the built environment were protected with insurance and building codes.

c$.$ People were conceding some property rights for individual security.

d$.$ Racial inequality was eliminated thanks to eminent domain rules protecting property rights.

e$.$ A$,$ B$,$ and C

f$.$ A$,$ B$,$ and D