Answer:
a. Experiencing disequilibrium
Step-by-step explanation:
Equilibrium and disequilibrium are the two types of developmental stages of a child. Under the disequilibrium stage, the child learns new things and new abilities. Also, he becomes anxious, stressed and uneasy about the things around him. It can be referred to as the period of the struggle of the child which is difficult to manage for him. In the above case, for John is became very puzzling about the working of the earth. This is an example of disequilibrium.