Which of the following is not a factor that has contributed to the rapid population growth

Which of the following is not a factor that has contributed to the rapid population growth？

A．Now, there are no wars and people live in a peaceful world.

B．More children can live to their adulthood and have their own children.

C．People live longer now than in the past.

D．People immunize many fatal diseases of which many people died.

请帮忙给出正确答案和分析，谢谢！