Final answer:
The expression "more buildings are torn down than fall down" refers to the enforcement of building codes.
Step-by-step explanation:
The expression "more buildings are torn down than fall down" refers to 3) the enforcement of building codes. It suggests that the demolition or tearing down of buildings is more common than buildings actually collapsing due to natural causes or decay. This expression highlights the importance of building codes, regulations, and inspections to ensure the safety and compliance of structures.