Cousins Emma and Miguel are each given 5 ounces of apple juice by their grandmother. Emma's juice is served in a tall, thin glass and Miguel's is served in a short, wide glass. Miguel complains that Emma has more juice than he does. According to Piaget, how old are Emma and Miguel likely to be?
A. 5 years old
B. 7 years old
C. 9 years old
D. 11 years old