Not sure this is a physics question (probably biology). Anyway, the correct answer is A): "Plasticity helps us to adapt to our environment. It also generally decreases with age". Plasticity is the ability to adapt to the environment. Since this ability is linked with brain functions, and brain functions worsen with age, then plasticity decreases with age.
Assume both children bodies are point particles. The total moment of inertia about the rotation axis of 2 points particles of mass 16 kg and 25 kg at 1.5 m arm length is
where are the masses of 2 children are their distance to the center of rotation
