Passage Summary: Economists worry that part-time workers might take over full-time jobs because they are cheaper, but since part-timers are usually less happy and less productive, companies probably won't make the switch.

Conclusion: Full-time employees are not actually in significant danger of being replaced by part-time workers.

Reasoning: Job efficiency is linked to job satisfaction, and since part-time workers are generally less satisfied than full-time ones, they are less efficient and thus less attractive to employers.

Analysis: This argument functions by creating a conflict between two different economic pressures: cost-saving and efficiency. While part-time workers might be cheaper, the author introduces a premise that links their high turnover to low satisfaction and, consequently, low efficiency. If we accept that companies prioritize efficiency, the threat of replacement vanishes. Look for an answer that completes the logic by dismissing the threat to full-time jobs. It’s a classic 'quality over quantity' argument where the author bets on the value of a happy worker.