Falling death rate boosts growth and shifts age structure older

Steps:

• Population change = births - deaths; a fall in death rate increases net growth, causing population rise.
• Lower deaths mean more individuals survive to older ages, increasing the elderly proportion.
• Birth rate unchanged (ceteris paribus) keeps young cohorts stable, so overall population ages.
• Evaluate options: only falling death rate satisfies both increase and aging.

Why B is correct:

• Per demographic transition theory, declining mortality with stable fertility raises population size and median age as survival extends lifespans without adding youth.

Why the others are wrong:

• A: Fall in birth rate slows or reverses growth, shrinking population without aging it significantly.
• C: Rise in both rates may stabilize or reduce population; higher deaths prevent aging by shortening lifespans.
• D: Rise in death rate and fall in birth rate accelerate population decline, reducing size and potentially skewing younger via higher infant mortality.

Final answer: B