Retirement age directly impacts current workforce participation

Steps:

• Define labour force as working-age individuals (typically 15-64 or 16-65) who are employed or seeking work.
• Assess each option's effect on current vs. future labour force size.
• Identify immediate changes: those affecting existing participants now.
• Select option causing quick exit from workforce.

Why C is correct:

• Reducing retirement age forces current workers to leave the labour force earlier, per standard labour economics definition of participation rates tied to age cohorts.

Why the others are wrong:

• A: Smaller families reduce future population growth but do not immediately shrink the existing labour force.
• B: Lower birth rates decrease future entrants but have no instant effect on current size.
• D: Higher net immigration adds working-age people, increasing the labour force immediately.

Final answer: C