The core concept tested here is the understanding of how new habits are formed according to brain research. The correct answer is B, as the passage emphasizes that new habits require conscious effort to develop, as indicated by phrases like 'we consciously develop new habits'. Option A is incorrect because it contradicts the idea that effort is needed. Option C is wrong because it suggests that old habits are easily replaced without conscious effort, which is not supported by the passage. Option D is incorrect because it misrepresents the process of forming new habits, which involves creating new pathways rather than bypassing old ones.