Smart growth is a new trend in urban planning that

uses all natural materials to build structures
uses alternative energy resources
sets growth boundaries around cities and preserve open spaces
encourages the building of new structures rather than renovating old structure

I think the correct answer from the choices listed above is the third option. Smart growth is a new trend in urban planning that sets growth boundaries around cities and helps preserve open spaces. Smart growth is an urban planning and transportation theory that concentrates growth in compact walkable urban centers to avoid sprawl.