**Core Concept**: Conjunction usage (how vs. that/whether/why). **Analysis**: - **Correct Answer (B)**: 'How' introduces a clause explaining the *manner* of habit adoption, fitting the focus on unconscious processes. - **Error Options**: - A. 'That' would state a fact but omit the mechanism. - C. 'Whether' introduces doubt about occurrence, irrelevant here. - D. 'Why' addresses causation, not the method. **Key Insight**: The verb 'focus on' requires a conjunction clarifying *process* (how), not just existence. **Common Pitfall**: Confusing 'how' (method) with 'why' (reason).