Question

Today, the world's population is younger than ever due to ______________________.

Answer 1

growing numbers of young people in developing countries

Answer 2

The choices can be found elsewhere and as follows:

aging populations of developed countries
longer life expectancies
growing numbers of young people in developing countries
access to penicillin

I think the correct answer would be the third option. Today, the world's population is younger than ever due to growing numbers of young people in developing countries. Hope this answers the question.