Considering Piaget's Theory of Cognitive Development, We Would Expect a Student

Considering Piaget's theory of cognitive development, we would expect a student in the concrete operational stage to have the greatest difficulty with which one of the following questions?

A) An apple pie is cut into 4 pieces.A blueberry pie of the same size is cut into 12 pieces.How many pieces of blueberry pie do you need to have the same amount as 3 pieces of the apple pie?
B) How are an apple and a blueberry alike?
C) If we have one row of blueberries arranged like so: o o o o o o and another row of blueberries arranged like so: o o o o o o
Then does one row have more blueberries than the other?
D) If you have 8 Macintosh apples and 2 Jonathan apples, then do you have more Macintoshes or more apples?