What can smooth uncontrolled growth and move toward more ecologically sound growth? 

A)  discouraging mixed use zoning 
B)  taxing buildings rather than land 
C)  promoting high-density clusters 
D)  issuing free building permits

Promoting high-density clusters can help smooth uncontrolled growth and move toward more ecologically sound growth by reducing urban sprawl and preserving open spaces. This approach encourages the development of compact, walkable communities that are designed to be more transit-friendly and require less energy and resources to operate. It also helps to reduce the environmental impact of development by clustering buildings and infrastructure in a concentrated area. Discouraging mixed-use zoning can limit the diversity of the community and increase traffic, and issuing free building permits can encourage uncontrolled growth. Taxing buildings rather than land may incentivize property owners to demolish buildings rather than retrofitting them for sustainability.