Passage Summary: Common sense is just a bunch of ideas that have worked over time. As we find better ideas, they eventually replace the old ones, but because this happens slowly, common sense is never fully up to date.

Reasoning: Common sense is defined as a collection of useful, tested theories that progress as better theories replace older ones; however, because this replacement process is slow, common sense always retains some outdated theories.

Analysis: Since this is a Must Be True question, we are looking for a deduction that is strictly supported by the premises. The stimulus establishes a persistent lag: new theories are developed, but common sense absorbs them slowly, leading to the constant presence of obsolete theories. You should look for an answer choice that reflects this inherent delay or the idea that common sense is never perfectly synchronized with the most current, useful theories available.