More than 3,300 adolescents from 12 countries responded to the question about how many children they would love to have in the future. in most countries, on average, adolescents preferred:

I believe the answer is: 2-3 children.
For most people, these number of children is seem as ideal because they wanted their children to grow up with close relatives that might help them in the future. On top of that, most of them also want to try to have both a female and boy children

Ibelieve that the answer is (a).