Five-year-old Marco complains that his slice of cake is smaller than Maria's, his 10-year-old sister. But she explains, "Look, your slice is skinnier, but it's taller. So we really have the same amount"

Which aspect of concrete operational reasoning does Maria's explanation use?
A) decentered thought
B) seriation
C) class inclusion
D) dynamic transformation

A) decentered thought. Maria illustrates her ability for decentered thought by paying attention to both the width and height of the cake, while her brother Marco focuses his attention on only one dimension, the height.