Aiza Is Upset Because She Is Convinced That Her Brother's

Aiza is upset because she is convinced that her brother's cookie is bigger than hers.Her dad quickly breaks Aiza's cookie in two and tells her that she now has "more cookie." If Aiza is satisfied by this,how would Piaget explain her response?

A) She has not yet mastered object permanence.
B) She understands object permanence.
C) She does not yet understand conservation.
D) She has mastered conservation.