Which of the following factors least explains the fast-growing population in Africa?

Population growth occurs when birth rates exceed death rates. The factors that explain Africa's fast-growing population are those that either increase births or reduce deaths.

Control of diseases directly reduces mortality, meaning more people survive to adulthood and old age. A decline in death rate has the same effect: fewer people die each year, so the population grows faster. The education of women in Africa is still relatively low in many regions, and lower female education is strongly associated with higher birth rates, because women with less education tend to marry earlier and have more children. So low levels of female education help explain high population growth.

Improvement in transportation, however, does not directly cause population to grow. Better roads and railways improve the movement of goods and people but do not significantly increase birth rates or reduce death rates. While improved transport can help deliver medical supplies, the transport improvement itself is not a demographic factor that explains rapid population growth.

Of all the options, improvement in transportation has the weakest direct connection to population increase and therefore least explains Africa's fast-growing population.