Why Does Human Population Growth Typically Start Slow and Then

Why does human population growth typically start slow and then accelerate dramatically?

A) Fewer people at first produce fewer new people, but once there are many people, many new people are produced, too.
B) Fewer people will result in a lower birth rate.
C) People get better at exploiting resources.
D) It follows a j-shaped curve.
E) Countries go from being developing to developed.