Among 10-year-old children in 1900, only 1 in had all four of their grandparents still living.

25

Explanation:

This number is significantly lower compared to today's society.

At that time  lack of food resources , inability to medically solve various type of illness and war that keep occurring contribute a lot to the death of World's population.

This make a lot of people died at a very young age, so very few of them actually able to live long enough to see their grand children.

answer; elasticity of the lungs decreases;