Final answer:
Children in the preoperational stage are commonly observed being guided by appearances, as they have not yet grasped the concept of conservation.
Step-by-step explanation:
The characteristic commonly observed in children during the preoperational stage is c) Being guided by appearances. During this stage, children do not yet have a developed understanding of conservation; they are unable to grasp that changing the appearance of an object does not alter its mass, volume, or number if nothing is added or removed. For instance, in Piaget's demonstration with the pizza, Kenny mistakenly believes he has more pizza since his single slice is cut into smaller pieces as opposed to his sister's larger, but undivided, slice. This illustrates how children in the preoperational stage focus on the immediate visual aspects of an object rather than its actual properties.