Read the excerpt and answer the question. World population is projected to grow from 6.1 billion in 2000 to 8.9 billion in 2050, increasing
therefore by 47 per cent. The average annual population growth rate over this half-century will be 0.77
per cent, substantially lower than the 1.76 per cent average growth rate from 1950 to 2000.
World Population to 2300, Department of Economic and Social Affairs, United Nations, 2004
Which factor will contribute MOST to this change in the growth rate?
an improvement in urban infrastructure
a decrease in life expectancies
an increase in infant mortality
a fall in fertility rates