During the preoperational stage, children struggle with problems as they focus on one dimension and ignore changes in other dimensions. for example, laying out five candies close together versus spread out will likely lead a 2- to 7-year-old to state that the second layout has more candy (even though the actual number of candies is the same).

Conservation.

Explanation:

Swiss psychologist Jean Piaget gave four development stages for the cognitive development during which children adapt and adjust to their environment according to their capabilities. He said that a child cannot distinguish between the same quantity when they were distinguished by the container, shape, or size, in their pre-operational stage. This process of determining the quantity even while making adjustments to the shape, size or the containers refers to the conservation. The logical reasoning to solve these problems comes in the concrete operational stage.

i am pretty sure it is d.